Letteratura scientifica selezionata sul tema "Small space-Time scales"
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Articoli di riviste sul tema "Small space-Time scales"
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Andresen, Bjarne, e Christopher Essex. "Thermodynamics at Very Long Time and Space Scales". Entropy 22, n. 10 (28 settembre 2020): 1090. http://dx.doi.org/10.3390/e22101090.
Testo completoAbstract (sommario):
Any observation, and hence concept, is limited by the time and length scale of the observer and his instruments. Originally, we lived on a timescale of minutes and a length scale of meters, give or take an order of magnitude or two. Therefore, we devloped laboratory sized concepts, like volume, pressure, and temperature of continuous media. The past 150 years we managed to observe on the molecular scale and similarly nanoseconds timescale, leading to atomic physics that requires new concepts. In this paper, we are moving in the opposite direction, to extremely large time and length scales. We call this regime “slow time”. Here, we explore which laboratory concepts still apply in slow time and which new ones may emerge. E.g., we find that temperature no longer exists and that a new component of entropy emerges from long time averaging of other quantities. Just as finite-time thermodynamics developed from the small additional constraint of a finite process duration, here we add a small new condition, the very long timescale that results in a loss of temporal resolution, and again look for new structure.
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Caltagirone, Jean-Paul. "Non-Fourier heat transfer at small scales of time and space". International Journal of Heat and Mass Transfer 160 (ottobre 2020): 120145. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2020.120145.
Testo completo
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Mandapaka, P. V., P. Lewandowski, W. E. Eichinger e W. F. Krajewski. "Multiscaling analysis of high resolution space-time lidar-rainfall". Nonlinear Processes in Geophysics 16, n. 5 (24 settembre 2009): 579–86. http://dx.doi.org/10.5194/npg-16-579-2009.
Testo completoAbstract (sommario):
Abstract. In this study, we report results from scaling analysis of 2.5 m spatial and 1 s temporal resolution lidar-rainfall data. The high resolution spatial and temporal data from the same observing system allows us to investigate the variability of rainfall at very small scales ranging from few meters to ~1 km in space and few seconds to ~30 min in time. The results suggest multiscaling behaviour in the lidar-rainfall with the scaling regime extending down to the resolution of the data. The results also indicate the existence of a space-time transformation of the form t~Lz at very small scales, where t is the time lag, L is the spatial averaging scale and z is the dynamic scaling exponent.
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Berndtsson, Ronny, Kenji Jinno, Akira Kawamura, Magnus Larson e Janusz Niemczynowicz. "Some Eulerian and Lagrangian statistical properties of rainfall at small space-time scales". Journal of Hydrology 153, n. 1-4 (gennaio 1994): 339–55. http://dx.doi.org/10.1016/0022-1694(94)90198-8.
Testo completo
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Tzou, D. Y. "A Unified Field Approach for Heat Conduction From Macro- to Micro-Scales". Journal of Heat Transfer 117, n. 1 (1 febbraio 1995): 8–16. http://dx.doi.org/10.1115/1.2822329.
Testo completoAbstract (sommario):
A universal constitutive equation between the heat flux vector and the temperature gradient is proposed to cover the fundamental behaviors of diffusion (macroscopic in both space and time), wave (macroscopic in space but microscopic in time), phonon–electron interactions (microscopic in both space and time), and pure phonon scattering. The model is generalized from the dual-phase-lag concept accounting for the lagging behavior in the high-rate response. While the phase lag of the heat flux captures the small-scale response in time, the phase lag of the temperature gradient captures the small-scale response in space. The universal form of the energy equation facilitates identifications of the physical parameters governing the transition from one mechanism (such as diffusion or wave) to another (the phonon–electron interaction).
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Jinno, Kenji, Akira Kawamura, Ronny Berndtsson, Magnus Larson e Janusz Niemczynowicz. "Real-time rainfall prediction at small space-time scales using a two-dimensional stochastic advection-diffusion model". Water Resources Research 29, n. 5 (maggio 1993): 1489–504. http://dx.doi.org/10.1029/92wr02849.
Testo completo
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Hatch, D. R., F. Jenko, V. Bratanov e A. Bañón Navarro. "Phase space scales of free energy dissipation in gradient-driven gyrokinetic turbulence". Journal of Plasma Physics 80, n. 4 (6 maggio 2014): 531–51. http://dx.doi.org/10.1017/s0022377814000154.
Testo completoAbstract (sommario):
A reduced four-dimensional (integrated over perpendicular velocity) gyrokinetic model of slab ion temperature gradient-driven turbulence is used to study the phase-space scales of free energy dissipation in a turbulent kinetic system over a broad range of background gradients and collision frequencies. Parallel velocity is expressed in terms of Hermite polynomials, allowing for a detailed study of the scales of free energy dynamics over the four-dimensional phase space. A fully spectral code – the DNA code – that solves this system is described. Hermite free energy spectra are significantly steeper than would be expected linearly, causing collisional dissipation to peak at large scales in velocity space even for arbitrarily small collisionality. A key cause of the steep Hermite spectra is acritical balance– an equilibration of the parallel streaming time and the nonlinear correlation time – that extends to high Hermite numbern. Although dissipation always peaks at large scales in all phase space dimensions, small-scale dissipation becomes important in an integrated sense when collisionality is low enough and/or nonlinear energy transfer is strong enough. Toroidal full-gyrokinetic simulations using theGenecode are used to verify results from the reduced model. Collision frequencies typically found in present-day experiments correspond to turbulence regimes slightly favoring large-scale dissipation, while turbulence in low-collisionality systems like ITER and space and astrophysical plasmas is expected to rely increasingly on small-scale dissipation mechanisms. This work is expected to inform gyrokinetic reduced modeling efforts like Large Eddy Simulation and gyrofluid techniques.
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KOGAN, YAN I. "THE R→α′/R SPACE-TIME DUALITY FROM THE 2+1 POINT OF VIEW". Modern Physics Letters A 06, n. 06 (28 febbraio 1991): 501–15. http://dx.doi.org/10.1142/s0217732391000518.
Testo completoAbstract (sommario):
The duality between the large and small compactification radii in string theory (bosonic) is considered in the open topological membrane theory. The 2+1 analog of this R→α′/R duality is the duality between large and small scales in the corresponding topologically massive gauge theory with the spontaneous breaking of gauge invariance. This 2+1 duality is a consequence of the equivalence between the Chern-Simons theory with the mass term and the topologically massive gauge theory.
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Fiscaletti, D., B. Ganapathisubramani e G. E. Elsinga. "Amplitude and frequency modulation of the small scales in a jet". Journal of Fluid Mechanics 772 (8 maggio 2015): 756–83. http://dx.doi.org/10.1017/jfm.2015.227.
Testo completoAbstract (sommario):
The present study is an experimental investigation of the relationship between the large- and small-scale motions in the far field of an air jet at high Reynolds number. In the first part of our investigation, the analysis is based on time series of hot-wire anemometry (HWA), which are converted into space series after applying the Taylor hypothesis. By using a spectral filter, two signals are constructed, one representative of the large-scale motions ($2{\it\lambda}_{T}-L$, where ${\it\lambda}_{T}$ is the Taylor length scale, and $L$ is the integral length scale) and the other representative of the small-scale motions ($1.5{-}5{\it\eta}$, where ${\it\eta}$ is the Kolmogorov length scale). The small-scale signal is found to be modulated both in amplitude and in frequency by the energy-containing scales in an analogous way, both at the centreline and around the centreline. In particular, for positive fluctuations of the large-scale signal, the small-scale signal is locally stronger in amplitude (amplitude modulation), and it locally exhibits a higher number of local maxima and minima (frequency modulation). The extent of this modulation is quantified based on the strength of the large-scale fluctuations. The response of the small-scale motions to amplitude modulation can be considered instantaneous, being on the order of one Kolmogorov time scale. In the second part of our investigation we use long-range ${\it\mu}$PIV to study the behaviour of the small-scale motions in relation to their position in either high-speed or low-speed regions of the flow. The spatially resolved velocity vector fields allow us to quantify amplitude modulation directly in physical space. From this direct estimation in physical space, amplitude modulation is only 25 % of the value measured from HWA. The remaining 75 % comes from the fixed spectral band filter used to obtain the large- and small-scale signals, which does not consider the local convection velocity. A very similar overestimation of amplitude modulation when quantified in the time-frame is also obtained analytically. Furthermore, the size of the structures of intense vorticity does not change significantly in relation to the large-scale velocity fluctuation, meaning that there is no significant spatial frequency modulation. The remaining amplitude modulation in space can be explained as a statistical coupling between the strength of the structures of vorticity and their preferential location inside large-scale high-velocity regions. Finally, the implications that the present findings have on amplitude and frequency modulation in turbulent boundary layers (TBLs) are discussed.
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Wisniewski, W. Z. "Small telescopes and research from space". Symposium - International Astronomical Union 118 (1986): 323–24. http://dx.doi.org/10.1017/s0074180900151708.
Testo completoAbstract (sommario):
The number of artificial satellites dedicated to astrophysical research is increasing rapidly. Nearly 30 satellites currently under development or in the early planning stages will be in orbit within 10–12 years and will have more sensitive detectors and better data-processing technology as a result of current research. Many of the galactic and extragalactic objects discovered by the new technology are variable on surprisingly short time scales ranging from sub-seconds to many months. The new variable objects include but are not confined to: neutron and binary stars; quasars (and associated active centers of galaxies); newborn infrared stars and associated clouds; the coronal activity of main sequence stars; cataclysmic variables (white dwarfs in binaries); and novae, supernovae and remnants. We now realize that the short time-scale variations of many unusual stars and active galactic nuclei demand that ground and space data be taken as close in time as possible and that they be carefully planned and coordinated.
Tesi sul tema "Small space-Time scales"
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Henry, Quentin. "Apport de l’expérimentation aux petites échelles spatiales et temporelles sur l’étude du comportement mécanique des céramiques à microstructure contrôlée soumises à des sollicitations dynamiques". Electronic Thesis or Diss., Paris, ENSAM, 2024. http://www.theses.fr/2024ENAME052.
Testo completoAbstract (sommario):
Dans le cadre de l'allègement des structures de blindage mécanique, les céramiques se distinguent comme des matériaux de choix en raison de leur grande résistance à la compression, tout en étant plus légères que les métaux conventionnellement utilisés. Certains modèles micromécaniques suggèrent que l'augmentation apparente des propriétés mécaniques des matériaux fragiles sous des sollicitations dynamiques résulte de l'interaction entre la vitesse de chargement et la vitesse de propagation des fissures dans une structure hétérogène. Cependant, cette hypothèse n'a pas encore été confirmée par des preuves expérimentales textit{in situ}. Une approche empirique a été proposée pour vérifier cette hypothèse et montrer l’influence de la microstructure des céramiques sur la sensibilité de leur réponse mécanique à la vitesse de déformation. Cette approche expérimentale doit considérer l’ensemble des effets dynamiques, notamment ceux liés à la propagation rapide des fissures. Une stratégie expérimentale a été élaborée pour mettre en évidence les mécanismes physiques induits par une sollicitation dynamique au sein d'une microstructure contrôlée.Pour maîtriser la microstructure, des pores ont été introduits dans une matrice d’alumine avec un contrôle précis de leur quantité, taille et morphologie. Il a été observé que les propriétés mécaniques diminuent à mesure que le taux de porosité augmente. À densité constante, les pores de grande taille sont particulièrement préjudiciables vis-à-vis des propriétés mécaniques.L'augmentation de la vitesse de déformation conduit à une augmentation des propriétés mécaniques apparentes. En employant des techniques conventionnelles de laboratoire sous des régimes dynamiques, et en les combinant à une analyse des fragments, il a été possible d’identifier le début de la zone transitoire où la contrainte à rupture des céramiques poreuses commence à augmenter. La compétition entre la propagation rapide des fissures et la cinétique de chargement décrite dans les modèles micromécaniques se reflète par la diminution plus importante de la taille des fragments des céramiques poreuses. L'ajout de pores entraîne une hausse de la densité des défauts critiques, ce qui facilite l'amorçage de fissures supplémentaires sous des contraintes dynamiques.L'analyse réalisée sous source synchrotron à l'ESRF a permis de suivre avec précision la cinétique de fissuration des céramiques ainsi que la réponse de la structure sous des sollicitations dynamiques. Les résultats obtenus, notamment la vitesse de propagation des fissures et les différents chemins de fissuration, offrent des références précieuses pour valider les approches numériques de modélisation de la rupture des matériaux fragiles. La propagation rapide des fissures génère des effets d'inertie, estimés par une approche numérique directe. Les résultats soulignent l'importance d'utiliser une telle méthode pour estimer l'énergie de rupture, sans quoi les effets dynamiques risquent d’être largement surestimés, compromettant ainsi l’intégrité des structuresCeramics stand out as materials of choice for lightening mechanical armor structures, thanks to their high compressive strength, while being lighter than conventionally used metals. Some micromechanical models suggest that the apparent increase in mechanical properties of brittle materials under dynamic loading results from the interaction between loading velocity and crack propagation velocity in a heterogeneous structure. However, no textit{in situ} experimental evidence has yet validated this hypothesis. An empirical approach has been proposed to verify this hypothesis and show the influence of ceramic microstructure on the sensitivity of their mechanical response to strain rate. This experimental approach must take account of all dynamic effects, particularly those linked to rapid crack propagation. The method envisaged for this thesis will put into perspective the effect of microstructure on the fragmentation process of ceramics at different strain rates.To control the microstructure, pores were introduced into an alumina matrix with precise control over their quantity, size and morphology. It was observed that mechanical properties decreased with increasing pore size. At constant density, large pores are particularly critical in terms of mechanical properties. An increase in strain rate leads to an increase in apparent mechanical properties. This sensitivity is even more pronounced in porous ceramics. The competition between rapid crack propagation and loading rates described in micromechanical models is reflected in the decrease in fragment size, which is more pronounced in porous ceramics. The introduction of pores leads to an increase in the density of critical defects, favoring the initiation of more cracks under dynamic loading. The analysis carried out under synchrotron source at ESRF enabled us to accurately track the fracture kinetics of the ceramics, as well as the response of the structure under dynamic loading. The results obtained, in particular the crack propagation velocity and the different fracture paths, provide valuable references for validating numerical approaches to modeling the fracture of brittle materials. This rapid crack propagation generates inertia effects, estimated by a direct numerical approach. The results underline the importance of using such a method to estimate fracture energy, otherwise dynamic effects could be greatly overestimated, compromising structural integrity
Libri sul tema "Small space-Time scales"
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Allen, Nicholas, Nick Groom e Jos Smith. Introduction. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198795155.003.0001.
Testo completoAbstract (sommario):
In 1967, Benoît Mandelbrot suggested a mathematical conundrum that involved answering the seemingly straightforward question, ‘How long is the coast of Britain?’1 The answer is surprisingly elusive and dependent on the scale at which one is looking. Increasing the scale unearths greater detail, time and time again, and so the answer grows the closer one looks. The problem is that any measure, at however small a scale, is forced to simplify complex ambiguities that might otherwise reveal further intricacies of their own. This was an entry-point to Mandlebrot’s writings on fractal geometry, but it also chimes with the very ecology and geomorphology of that coast itself, characteristically intricate, ambiguous, and changeable. Large-scale, ocean-facing landforms—such as capes and bays, estuaries, dunefields, and reefs—are well known to have, nestled within them, smaller and often dynamically mobile features such as longshore bars and troughs, berms and beach cusps, not to mention difficult-to-measure caves, inlets, tributaries, and salt marshes. Looking closer still are to be found the ripples, rills, and swash marks of a more minute scale; even within these are to be found the bioturbation structures of intertidal organisms: forms within forms, scales within scales, and worlds within worlds. In the way that it draws the attention down into such minute details as these, while at the same time drawing it up towards an expanse that suggests a space almost planetary in scale, the coast is a highly distinctive geographical environment. And yet it has all too often been overlooked, as if its peripheral relationship to the land has reinforced its peripheral treatment culturally....
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Isett, Philip. Mollification along the Coarse Scale Flow. Princeton University Press, 2017. http://dx.doi.org/10.23943/princeton/9780691174822.003.0018.
Testo completoAbstract (sommario):
This chapter shows how to construct the appropriate mollification of the Reynolds stress along the coarse scale flow. Unlike the velocity field, which was only mollified in the spatial variables and which earned its time-regularity through the Euler-Reynolds equation, the Reynolds stress must be mollified in both space and time. Mollification along the flow is consistent with the Galilean invariance of the equations. After considering the problem of mollifying the stress in time, the chapter explains how the stress can be mollified in both space and time. It then chooses the mollification parameters, requiring that the error term generated by this mollification constitutes a small fraction of the allowable stress. It also derives estimates for the coarse scale flow as well as transport estimates for the mollified stress.
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Martin, S. Rebecca, e Stephanie M. Langin-Hooper, a cura di. The Tiny and the Fragmented. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780190614812.001.0001.
Testo completoAbstract (sommario):
Miniature and fragmentary objects are both remarkably fascinating and easily dismissed. Tiny scale entices users with visions of Lilliputian worlds. The ambiguity of fragments intrigues us, offering vivid reminders of the transitory nature of reality. Yet, the standard scholarly approach to such objects has been to see them as secondary, incomplete things, designed primarily to refer to a complete and often life-sized whole. This volume offers a series of fresh perspectives on the familiar concepts of the tiny and the fragmented, in chapters ranging in focus from Neolithic Europe to Pre-Columbian Honduras to the Classical Mediterranean and Ancient Near East. Diverse in scope, the volume is united in considering the little and broken things of the past as objects in their own right. When a life-sized or whole thing is made in a scaled-down or partial form, deliberately broken as part of its use, or considered successful by ancient users only if it shows some signs of wear, it challenges our expectations of representation and wholeness. Overall, this volume demands a reconsideration of the social and contextual nature of miniaturization, fragmentation, and incompleteness. These were more than just ancient strategies for saving space, time, and resources. Rather, they offered new possibilities of representation, use, and engagement—possibilities unavailable with things that were life size or more conventionally “complete.” It was because of, rather than in spite of, their small or partial state that these objects were valued parts of the personal and social worlds they inhabited.
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Sears, David. The Last Epic Naval Battle. Greenwood Publishing Group, Inc., 2005. http://dx.doi.org/10.5040/9798400676727.
Testo completoAbstract (sommario):
Often overshadowed by other Pacific War engagements such as Midway or Guadalcanal, the Battle of Leyte Gulf was characterized by some of the most gallant hours in seagoing history: the U.S. Navy's defeat of the combined Japanese fleet during the invasion of the Philippines in October 1944. Involving more ships than even the gargantuan First World War Battle of Jutland and two hundred thousand men, it was the biggest naval battle in world history. It marked the last time that huge capital ships fought within sight and sound of each other. Using the personal accounts of the men who were there, Sears tells this mammoth and compelling story. This moving tale uses personal accounts of the veterans who achieved victory in the biggest and last great naval battle, largely fought with aging ships, untested reserve crews, and teenaged combat aircraft pilots. Often overshadowed by other Pacific War engagements such as Midway or Guadalcanal, the Battle of Leyte Gulf was characterized by some of the most gallant hours in seagoing history: the U.S. Navy's defeat of the combined Japanese fleet during the invasion of the Philippines in October 1944. Involving more ships than even the gargantuan First World War Battle of Jutland and two hundred thousand men, it was the biggest naval battle in world history. It marked the last time huge capital ships fought within sight and sound of each other. Using the personal accounts of the men who were there, Sears tells this mammoth and compelling story. The Battle of Leyte Gulf could have been the Pacific War's Battle of the Bulge. In a space of 12 hours, Japan, a beaten, cornered enemy, was able to devise and execute a strategy that very nearly pierced the heart of America's war machine. The real margin of victory would come from surprising quarters: from aging ships risen from the graveyard of the war's infamous first day; from small, hastily constructed ships with largely untested reserve crews; from fragile support ships never intended to be anywhere near battles of this scale; and from combat aircraft piloted by teenagers.
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Wojewodzic, Tomasz. Procesy dywestycji i dezagraryzacji w rolnictwie o rozdrobnionej strukturze agrarnej. Publishing House of the University of Agriculture in Krakow, 2017. http://dx.doi.org/10.15576/978-83-66602-31-1.
Testo completoAbstract (sommario):
The turn of the 20th and 21st centuries has been a very dynamic period of change in Poland and around the world; also a period of change in thinking about the economy and agriculture. The present work is a study of the decline, divestments and development of agriculture in the areas of fragmented farming structure. The reflections presented herein, upon the processes of the remodelling of agrarian structures, of divestments in farming, and disagrarisation, are mostly anchored in the achievements of the theory of spatial economy (land management), and the microeconomic theories of choice, including the theory of an agricultural holding (farm) and land rent theories. The work focuses on the economic issues of remodelling the agrarian structure, but due to the nature of the issues discussed herein, specifically in relation to family-owned farms, the social and environmental aspects also needed to be taken into account – in response to the need for a heterogeneous approach, which is increasingly stressed in economic sciences today. The main objective of the research was to diagnose and assess the scale and scope of the mechanisms and processes that inform the decline and growth of agricultural holdings in the areas with fragmented farming structure. The study covered the area comprising four regions (provinces) of south-eastern Poland, which – according to the FADN nomenclature – form the macro region of Małopolska and Pogórze. The study of subject literature has been enriched with an analysis of available statistics; data from the Farm Accountancy Data Network (FADN); information obtained from the Department of Programming and Reporting at the Agency for Restructuring and Modernisation of Agriculture; and author’s own research conducted among farm owners. The information thus obtained made it possible to: • Determine the theoretical premises for the spatial diversity of agriculture, and the role of small farms in the shaping of agrarian structure. • Adapt the concept of “divestment” for the description and analysis of the phenomena occurring in agriculture. • Indicate the role and importance of the processes of divestment and disagrarisation in the restructuring of agriculture. • Assess the natural, social and economic determinants of the process of restructuring agriculture in areas with fragmented farming structure. • Assess selected aspects of economic efficiency of agriculture in areas with fragmented farming structure, with the focus on small and micro farms. • Carry out an ex ante evaluation of the impact of agricultural policy instruments on the process of restructuring of agriculture in the macro region of Małopolska and Pogórze. • Identify the indicators of decline and fall, and barriers to the liquidation of farms. • Assess the relationship between the level of socio-economic development, the structure of farming, and the quality of agricultural production space in a given territorial unit, versus the intensity of the economic and production disagrarisation processes in agricultural holdings. • Propose targeted solutions conducive to the improvement of the farming structure in areas with a high framentation of agriculture. Observation of the processes occurring in agriculture, and the scientific theories created on the basis thereof, have shown that even the smallest farms have a chance to continue in existence, provided that we are able to positively verify their adaptation to the changing conditions in the environment. Carrying out farming activity is a prerequisite for implementing the economic, social and environmental functions associated with family farms. At the same time, based on the analyses performed, we need to assume that the advanced processes of the production and economic disagrarisation of agricultural holdings are to a greater extent determined by the anatomical features of agriculture, and by the natural conditions, than by the level of socio-economic development of the given territorial unit. In the current economic climate, the remodelling of the agrarian structure is only possible with the active participation of the institutions responsible for the creation of economic growth and agricultural policy development. It is extremely important from the point of view of environmental protection, and the viability of rural areas, to support small farms engaged in agricultural activities, and to introduce such instruments that will enable the replacement of an economic collapse with divestments, carried out in a planned manner, and allowing for thus released agricultural resources to find alternative application in units with a higher development potential. The area of theoretical research requiring further exploration includes the issues such as transactional costs of the liquidation of agricultural holdings, and the assessment of the economic effectiveness of conducting divestments.
Capitoli di libri sul tema "Small space-Time scales"
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McCauley, Joseph L. "Universality in Fully Developed Chaos, and Statistics at Small Scales in Turbulence". In Spontaneous Formation of Space-Time Structures and Criticality, 395–419. Dordrecht: Springer Netherlands, 1991. http://dx.doi.org/10.1007/978-94-011-3508-5_29.
Testo completo
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Dessertine, Anna. "Spatializing Social Change: Artisanal and Small-Scale Gold Mining in Upper Guinea". In Methodological Approaches to Societies in Transformation, 213–35. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-65067-4_9.
Testo completoAbstract (sommario):
AbstractThis chapter proposes a spatial perspective on the analysis of social change in the making via a study of artisanal and small-scale gold-mining sites in Guinea based on twenty-two months of fieldwork between 2011 and 2019 in the region of Upper Guinea, where increasing numbers of inhabitants have been circulating between artisanal and small-scale mining sites to search for gold since the price of gold rose between 2008 and 2012. The chapter starts by discussing artisanal and small-scale mining spaces through the notion of hotspots of transition, insisting on their liminal character. This liminality is analyzed as a spatial framework in which new opportunities emerge regarding gender—women’s adoption of what is considered masculine behavior, for instance—and where instantaneity is more privileged than continuity in some actions, such as those associated with consumption. More generally, it shows how the potential for change in artisanal and small-scale mining spaces is closely linked to their ephemeral nature. The relationship between space and temporality is more explicitly discussed in the second part of the chapter, which explores how the ephemerality of artisanal and small-scale mining spaces has recently been challenged by the Guinean government’s move to control mining mobility and fix mining sites spatially by delimiting legal mining territories. Since 2015–2016, multiple military operations have been conducted to expel miners from land for which the Guinean State has given industrial companies legal permits to prospect for and mine gold. This part of the chapter analyzes the socio-spatial consequences of this situation and shows that perceptions of time and of social change are constructed by the forms that space take.
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Huston, David L., Robert B. Trumbull, Georges Beaudoin e Trevor Ireland. "Light Stable Isotopes (H, B, C, O and S) in Ore Studies—Methods, Theory, Applications and Uncertainties". In Isotopes in Economic Geology, Metallogenesis and Exploration, 209–44. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-27897-6_8.
Testo completoAbstract (sommario):
AbstractVariations in the abundances of light stable isotopes, particularly those of hydrogen, boron, carbon, oxygen and sulfur, were essential in developing mineralization models. The data provide constraints on sources of hydrothermal fluids, carbon, boron and sulfur, track interaction of these fluids with the rocks at both the deposit and district scales, and establish processes of ore deposition. In providing such constraints, isotopic data have been integral in developing genetic models for porphyry-epithermal, volcanic-hosted massive sulfide, orogenic gold, sediment-hosted base metal and banded-iron formation-hosted iron ore systems, as discussed here and in other chapters in this book. After providing conventions, definitions and standards used to present stable isotope data, this chapter summarizes analytical methods, both bulk and in situ, discusses processes that fractionate stable isotopes, documents the isotopic characteristics of major fluid and rock reservoirs, and then shows how stable isotope data have been used to better understand ore-forming processes and to provide vectors to ore. Analytical procedures, initially developed in the 1940s for carbon–oxygen analysis of bulk samples of carbonate minerals, have developed so that, for most stable isotopic systems, spots as small as a few tens of μm are routinely analyzed. This precision provides the paragenetic and spatial resolution necessary to answer previously unresolvable genetic questions (and create new questions). Stable isotope fractionation reflects geological and geochemical processes important in ore formation, including: (1) phase changes such as boiling, (2) water–rock interaction, (3) cooling, (4) fluid mixing, (5) devolatilization, and (6) redox reactions, including SO2 disproportionation caused by the cooling of magmatic-hydrothermal fluids and photolytic dissociation in the atmosphere. These processes commonly produce gradients in isotopic data, both in time and in space. These gradients, commonly mappable in space, provide not only evidence of process but also exploration vectors. Stable isotope data can be used to estimate the conditions of alteration or mineralization when data for coexisting minerals are available. These estimates use experimentally- or theoretically-determined fractionation equations to estimate temperatures of mineral formation. If the temperature is known from isotopic or other data (e.g., fluid inclusion data or chemical geothermometers), the isotopic composition of the hydrothermal fluid components can be estimated. If fluid inclusion homogenization and compositional data exist, the pressure and depth of mineralization can be estimated. One of the most common uses of stable isotope data has been to determine, or more correctly delimit, fluid and sulfur sources. Estimates of the isotopic compositions of hydrothermal fluids, in most cases, do not define unequivocal sources, but, rather, eliminate sources. As an example, the field of magmatic fluids largely overlap that of metamorphic fluids in δ18O-δD space, but are significantly different to the fields of meteoric waters and seawater. As such, a meteoric or seawater origin for a fluid source may be resolvable, but a magmatic source cannot be resolved from a metamorphic source. Similarly, although δ34S ~ 0‰ is consistent with a magmatic-hydrothermal sulfur source, the signature can also be produced by leaching of an igneous source. Recent analytical and conceptual advances have enabled gathering of new types of isotopic data and application of these data to resolve new problems in mineral deposit genesis and geosciences in general. Recent developments such as rapid isotopic analysis of geological materials or clumped isotopes will continue to increase the utility of stable isotope data in mineral deposit genesis and metallogeny, and, importantly, for mineral exploration.
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Platzer, Paul, Bertrand Chapron e Pierre Tandeo. "Dynamical Properties of Weather Regime Transitions". In Mathematics of Planet Earth, 223–36. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-031-18988-3_14.
Testo completoAbstract (sommario):
AbstractLarge-scale weather can often be successfully described using a small amount of patterns. A statistical description of reanalysed pressure fields identifies these recurring patterns with clusters in state-space, also called “regimes”. Recently, these weather regimes have been described through instantaneous, local indicators of dimension and persistence, borrowed from dynamical systems theory and extreme value theory. Using similar indicators and going further, we focus here on weather regime transitions. We use 60 years of winter-time sea-level pressure reanalysis data centered on the North-Atlantic ocean and western Europe. These experiments reveal regime-dependent behaviours of dimension and persistence near transitions, although in average one observes an increase of dimension and a decrease of persistence near transitions. The effect of transition on persistence is stronger and lasts longer than on dimension. These findings confirm the relevance of such dynamical indicators for the study of large-scale weather regimes, and reveal their potential to be used for both the understanding and detection of weather regime transitions.
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Macek, Wiesław M. "On the Origin of the Universe: Chaos or Cosmos?" In 14th Chaotic Modeling and Simulation International Conference, 311–26. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-96964-6_21.
Testo completoAbstract (sommario):
AbstractI would like to consider the Universe according to the standard Big Bang model, including various quantum models of its origin. In addition, using the theory of nonlinear dynamics, deterministic chaos, fractals, and multifractals I have proposed a new hypothesis, Macek (The Origin of the World: Cosmos or Chaos? Cardinal Stefan Wyszyński University (UKSW) Scientific Editions, 2020). Namely, I have argued that a simple but possibly nonlinear law is important for the creation of the Cosmos at the extremely small Planck scale at which space and time originated. It is shown that by looking for order and harmony in the complex real world these modern studies give new insight into the most important philosophical issues beyond classical ontological principles, e.g., by providing a deeper understanding of the age-old philosophical dilemma (Leibniz, 1714): why does something exist instead of nothing? We also argue that this exciting question is a philosophical basis of matters that influence the meaning of human life in the vast Universe.
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Mulligan, Mark, Sophia Burke, Caitlin Douglas e Arnout van Soesbergen. "Methodologies to Assess and Map the Biophysical Effectiveness of Nature Based Solutions". In Water Security in a New World, 51–65. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-25308-9_4.
Testo completoAbstract (sommario):
AbstractNature based solutions to mitigate flooding (Natural Flood Management, NFM) can help address persistent flooding on smaller rivers that are beyond the reach of governmental grey infrastructure flood protection schemes and can also contribute to ‘green-grey’ solutions for larger rivers, recognising the many co-benefits of such nature-based solutions for nature and society. It is, however, vital that NFM interventions are carefully designed and fully tested for their effectiveness and cost-effectiveness so as not to waste valuable flood mitigation resources and to ensure that these solutions do not themselves exacerbate risks or become expensive to scale or maintain. Only through accessible, low cost approaches can this be achieved since each NFM project is usually rather small scale, low budget and unique in design and context.This chapter introduces newly developed methods for assessing the effectiveness of NFM with a focus on low-cost and open-access solutions. It highlights the opportunities and challenges of different monitoring and modelling methods, from physically-based spatial scenario models for assessing impacts of NFM interventions on flood risk to downstream assets, to using networks of low-cost environmental monitoring stations for direct measurement of effectiveness of specific interventions. Modelling is best suited to large scale strategic assessment of the optimal type, magnitude and locations of interventions, whereas assessment of the effectiveness of specific interventions is best achieved through a measurement approach or – where that is not possible – space-for-time substitution with comparable sites for which the intervention has already been applied and its effectiveness tested.
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Demoraes, Florent, Nicolas Ovtracht, Kamila Tabaka, Sarah Duché, Boris Mericskay e Camille Sieper. "The Spatial Dimension of “Pop-Up Cycle Paths” in Metropolitan Areas a Comparative Study of France and Colombia". In The Urban Book Series, 169–95. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-45308-3_8.
Testo completoAbstract (sommario):
AbstractThis chapter goes over how Covid-19 pandemic impacted in space and time on cycling infrastructure in four French cities (Grenoble, Lyon, Montpellier, and Rennes) which we have compared with Bogotá (Colombia). It shows that local authorities implemented different strategies to develop their networks during this unusual period running from 2020 to 2021. The sizeable task of researching, refining, harmonising, and comparing several sources was formalised to ensure reproducibility, and a typology drawn up to compare the five cities. Certain local authorities installed equipment mainly in central spaces, while others also extended infrastructure to the outskirts, in certain cases duplicating pre-existing cycling facilities. In some cities, such as Montpellier, Grenoble, and even more markedly Bogotá, low-income districts also benefited to a certain extent from pop-up cycling infrastructure. Concerning the extent of coverage, two years after the beginning of the pandemic, most of the pop-up cycling infrastructure in the cities under study had been dismantled, or else retained on the already dense parts of the network. In several cases pop-up tracks were used to make up for missing links in the pre-existing network. They also sometimes provided a way of improving certain connections, but given the small number of pop-up paths which became lasting facilities, they have not fundamentally expanded the scale of the networks as the pandemic recedes, nor have they made the cities significantly more cycle-friendly overall.
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Barrow, John D. "Organizing principles". In New Theories of Everything, 160–91. Oxford University PressNew York, NY, 2007. http://dx.doi.org/10.1093/oso/9780192807212.003.0007.
Testo completoAbstract (sommario):
Abstract The watcher of science is much impressed by the very large and the very small. The latest speculations about the inner space of elementary particles and the outer space of the astronomer’s universe dominate most contemplations of the ultimate stucture of the physical universe. Intuitively, we feel that the ultimate secrets of the Universe’s constitution must reside at the extremes of our scales of imagination. But there are extremes other than those of scale and time and temperature. There are extremes of complexity.
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Ahamed, Md Atik, e Qiang Cheng. "TimeMachine: A Time Series is Worth 4 Mambas for Long-Term Forecasting". In Frontiers in Artificial Intelligence and Applications. IOS Press, 2024. http://dx.doi.org/10.3233/faia240677.
Testo completoAbstract (sommario):
Long-term time-series forecasting remains challenging due to the difficulty in capturing long-term dependencies, achieving linear scalability, and maintaining computational efficiency. We introduce TimeMachine, an innovative model that leverages Mamba, a state-space model, to capture long-term dependencies in multivariate time series data while maintaining linear scalability and small memory footprints. TimeMachine exploits the unique properties of time series data to produce salient contextual cues at multi-scales and leverage an innovative integrated quadruple-Mamba architecture to unify the handling of channel-mixing and channel-independence situations, thus enabling effective selection of contents for prediction against global and local contexts at different scales. Experimentally, TimeMachine achieves superior performance in prediction accuracy, scalability, and memory efficiency, as extensively validated using benchmark datasets. Code availability: https://github.com/Atik-Ahamed/TimeMachine
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Bengtsson, J., K. Engelhardt, P. Giller, S. Hobbie, D. Lawrence, J. Levine, M. Vila e V. Wolters. "Slippin’ and slidin’ between the scales: the scaling components of biodiversity-ecosystem functioning relations". In Biodiversity and Ecosystem Functioning, 209–20. Oxford University PressOxford, 2002. http://dx.doi.org/10.1093/oso/9780198515708.003.0018.
Testo completoAbstract (sommario):
Abstract Whilst the problems of scale are well-known to most ecologists, many subdisciplines of ecology are still struggling with its central concepts-how the dimensions of space and time, and levels of organization, influence ecological patterns and processes (e.g. Peterson and Parker 1998; O’Neill and King 1998; Petersen and Hastings 2001; Schneider 2001). Individual ecologists may, at their own peril, ignore the problem and focus on one scale and one level of organization only. However, the synthesis of many individual studies con ducted at different scales requires a better under standing of the influence of scale on ecological processes. This is particularly evident in the study of biodiversity and ecosystem functioning. Although studying at least two levels-community and ecosystem-most research has been performed at small spatial and short temporal scales (Loreau et al. 2001; Naeem 2001), and it is not clear if such studies can be used to inform the public and policymakers about the large-scale consequences of biodiversity loss.
Atti di convegni sul tema "Small space-Time scales"
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Duque, Earl, Pankaj Jha, Jessica Bashioum e Sven Schmitz. "Turbulence Transport Phenomena in the Wakes of Wind Turbines". In Vertical Flight Society 70th Annual Forum & Technology Display, 1–16. The Vertical Flight Society, 2014. http://dx.doi.org/10.4050/f-0070-2014-9687.
Testo completoAbstract (sommario):
A true physical understanding of the subtleties involved in the recovery process of the wake momentum deficit downstream of utility-scale wind turbines in the atmosphere has not been obtained to date. While the wind energy community has now a better understanding of some of the effect of the atmospheric stability state on wind turbine power production and wake recovery within an array of wind turbines, available field data are, in general, not acquired at sufficient spatial and temporal resolution that would allow to dissecting some of the mysteries of wake turbulence. It is here that the Actuator Line Method (ALM) has evolved to become the technology standard in the wind energy community for modeling the wakes of single wind turbines as well as arrays of wind turbines and wind farms immersed in an atmospheric boundary-layer flow. This work presents the ALM embedded into an OpenFOAM-LES solver (ALM/LES) and applies it to two small wind farms, the first one consisting of an array of two NREL 5-MW turbines separated by seven rotor diameters in neutral and unstable atmospheric boundary-layer (ABL) flow and the second one consisting of five NREL 5-MW wind turbines arranged in two staggered arrays of two and three turbines, respectively, in unstable ABL flow. Detailed statistics involving power spectral density (PSD) of turbine power along with standard deviations reveal the effects of atmospheric turbulence and its space and time scales. Furthermore, the effect of turbulence generated directly by upstream wind turbines on the power response of downstream wind turbines is quantified. High-resolution surface data extracts in addition to selected Reynolds-stress statistics provide new insight into the complex recovery process of the wake momentum deficit governed by turbulence transport phenomena.
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Dawes, W. N. "Simulating Unsteady Turbomachinery Flows on Unstructured Meshes Which Adapt Both in Time and Space". In ASME 1993 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1993. http://dx.doi.org/10.1115/93-gt-104.
Testo completoAbstract (sommario):
The objective of this paper is to stimulate study of application of solution-adaptive methods to unsteady turbomachinery flows. First, the extension of an existing 3D unstructured mesh Navier-Stokes solver to cover unsteady flows is described. Then the basic method is validated for the classic case of vortex shedding from a cylinder. Next, the modification of the data structures of the algorithm into a strict parent-child hierarchy are described; this enables refinement and derefinement to take place sufficiently economically for mesh adaption to take place over time scales significantly smaller than the characteristic time scales of the unsteady flow. Application to the vortex shedding from a cylinder showed that the unsteady solution obtained on an adaptively (locally) refined mesh was essentially the same as that from a reference, uniformly (globally) refined mesh, both simulations predicting a Strouhal number of 0.20. By contrast, a basic unrefined mesh predicted a small but systematically lower shedding frequency and Strouhal number of 0.17. Finally, both Euler and Navier-Stokes solutions are obtained for the standard problem of the interaction of stator wakes with the following rotor row. The adaptively refined solution displays very good control over the wake resolution and minimises false smoothing of the wake structures as they propagate. Good qualitative agreement is observed in comparison with other published numerical simulations. It is concluded that the application of unstructured mesh methods which adapt both in time and space to unsteady flow problems is both viable and promising.
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Nandakumar, K., Pankaj Wahi e Anindya Chatterjee. "Infinite Dimensional Slow Modulations in a Delayed Model for Orthogonal Cutting Vibrations". In ASME 2008 9th Biennial Conference on Engineering Systems Design and Analysis. ASMEDC, 2008. http://dx.doi.org/10.1115/esda2008-59339.
Testo completoAbstract (sommario):
We apply the method of multiple scales (MMS) to a well known model of regenerative cutting vibrations in the large delay regime. By “large” we mean the delay is much larger than the time scale of typical cutting tool oscillations. The MMS upto second order for such systems has been developed recently, and is applied here to study tool dynamics in the large delay regime. The second order analysis is found to be much more accurate than first order analysis. Numerical integration of the MMS slow flow is much faster than for the original equation, yet shows excellent accuracy. The main advantage of the present analysis is that infinite dimensional dynamics is retained in the slow flow, while the more usual center manifold reduction gives a planar phase space. Lower-dimensional dynamical features, such as Hopf bifurcations and families of periodic solutions, are also captured by the MMS. Finally, the strong sensitivity of the dynamics to small changes in parameter values is seen clearly.
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Thompson, Lonny L., e Prapot Kunthong. "Stabilized Time-Discontinuous Galerkin Methods With Applications to Structural Acoustics". In ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-15753.
Testo completoAbstract (sommario):
The time-discontinuous Galerkin (TDG) method possesses high-order accuracy and desirable C-and L-stability for second-order hyperbolic systems including structural acoustics. C- and L-stability provide asymptotic annihilation of high frequency response due to spurious resolution of small scales. These non-physical responses are due to limitations in spatial discretization level for large-complex systems. In order to retain the high-order accuracy of the parent TDG method for high temporal approximation orders within an efficient multi-pass iterative solution algorithm which maintains stability, generalized gradients of residuals of the equations of motion expressed in state-space form are added to the TDG variational formulation. The resultant algorithm is shown to belong to a family of Pade approximations for the exponential solution to the spatially discrete hyperbolic equation system. The final form of the algorithm uses only a few iteration passes to reach the order of accuracy of the parent solution. Analysis of the multi-pass algorithm shows that the first iteration pass belongs to the family of (p+1)-stage stiff accurate Singly-Diagonal-Implicit-Runge-Kutta (SDIRK) method. The methods developed can be viewed as a generalization to the SDIRK method, retaining the desirable features of efficiency and stability, now extended to high-order accuracy. An example of a transient solution to the scalar wave equation demonstrates the efficiency and accuracy of the multi-pass algorithms over standard second-order accurate single-step/single-solve (SS/SS) methods.
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Sollier, Arnaud, e Emilien Lescoute. "Characterization of the ballistic properties of ejecta from laser shock-loaded samples using high resolution picosecond imaging". In 2019 15th Hypervelocity Impact Symposium. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/hvis2019-097.
Testo completoAbstract (sommario):
Abstract Anticipating the generation of high velocity debris from shock-loaded specimens and the damage that their impacts may cause to nearby equipment is a major safety issue in applications involving shock waves, such as pyrotechnics [1] or inertial confinement fusion (ICF) experiments on large scale laser facilities [2]. Microjetting is one of the processes governing such debris generation. It is due to the interaction of a shock wave with a free surface presenting geometrical defects such as pits, cavities, scratches, or grooves, leading to material ejection from these defects, in the form of thin jets expanding ahead of the main surface and breaking up into small particles [3]. Over the last few years, we have used laser shock loading in order to expand microjetting investigations over ranges of small spatial scales (μm scale), extremely high loading rates (~ 107 s-1) and very short pressure pulses (a few ns) [4-11]. Optical shadowgraphy and Photonic Doppler Velocimetry (PDV) have been used to measure both jet tip and planar surface velocities [4-6], while attempts to infer fragments size distributions, to be compared with model predictions, have been made using either fast transverse shadowgraphy [7] or ejecta recovery [8]. More recently, picosecond x-ray radiography has been used to provide estimates of the density gradients along the jets and of the total ejected mass at different times after shock breakout [9-11]. Here, we present the development of a new picosecond laser imaging diagnostic intended to overcome the limitations of our current transverse optical shadowgraphy setup. We describe our experimental setup and show the results of our first experiments performed using both visible (532 nm) and UV (355 nm) lightning of the sample. These results are compared to those obtained at LANL under high explosive loading using ultraviolet in-line Fraunhofer holography [12], and also to molecular dynamics (MD) simulations performed by our colleagues at lower space and time scales [15-18].
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Timmer, Alexander. "Open Thermodynamic Design: Exploring Dialectic Design Processes Through Mass Timber". In 2021 ACSA Teachers Conference. ACSA Press, 2021. http://dx.doi.org/10.35483/acsa.teach.2021.20.
Testo completoAbstract (sommario):
This paper examines a pedagogy that seeks to resist conventional approaches to the relationship between design and energy in architecture and instead advance our ability to address environmental concerns as designers through a dialogue with material utilizing criteria such as its mate¬rial sourcing, carbon footprint, and microclimate as drivers of design. This dialogue welcomes material agency as an active and critical participant in establishing the form and performance relationship. This paper articulates the process utilized in a three-credit seminar that asked students to design a mass timber cabin sited on a tree farm. The material for that cabin must be harvested from the site. This process asks the students to consider a series of dialectic relationships between the material, the site, the form, and the microclimate of their cabin. This reciprocal design process that repeatedly changes scales allows the students to engage environmental design as a systematic dialogue at multiple scales of time, space, and energy establishing an interconnected relationship between form and performance. This paper articulates the process by which students were given a site in which they harvest a set amount of timber and then use that material for the construction of a small mass timber cabin located on the very same site. Each itera-tion involved tumbling the cabin into different positions and asking the students to account for a new seasonal criterion. Each tumble reterritorializes earlier design decisions and requires the students to reevaluate those decisions under new material and climatological conditions. The cabin has three positions, summer, fall, and winter. Each position requires the students to address climate issues such as buoyancy ventilation, cross-ventilation, and the stratification of air. As the students make design changes, they harvest more lumber from the site. This creates a series of dialectic relationships at multiple temporal and spatial scales. Key issues, such as the number of trees cut down and the scale of their cabins, are tempered by discussions around embodied and sequestered carbon. This paper examines how these speculative projects ask students to consider design as part of an open thermodynamic system in which the building is a momentary physical manifestation of larger energy and material flows by speeding up certain.
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Vedula, Lalit, e N. Sri Namachchivaya. "Stochastically Perturbed Rotating Shafts". In ASME 2001 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/detc2001/vib-21450.
Testo completoAbstract (sommario):
Abstract The objective of this work is to study the long term effects of small symmetry-breaking, dissipative and noisy perturbations on the dynamics of a rotating shaft. Hamilton’s principle is used to derive the equations of motion and a one mode Galerkin approximation is applied to obtain a two-degree-of-freedom (four dimensional) model. A stochastic averaging method is developed to reduce the dimension of this four dimensional system. Making use of the interaction between the gyroscopic and dissipative forces and the separation of time scales, the original system is reduced to a one dimensional Markov process. Depending on the system parameters, the reduced Markov process takes its values on a line or a graph. For the latter case, the glueing conditions required to complete the description of the problem in the reduced space are derived. This provides a qualitatively accurate and computationally feasible description of the system. Analytical results are obtained for the mean first passage time problem. The stationary probability density is obtained by solving the Fokker Planck Equation (FPE). Finally, the qualitative changes in the stationary density as a result of varying the system parameters are described.
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Rega, Giuseppe, Walter Lacarbonara, Ali H. Nayfeh e Char-Ming Chin. "Multimodal Resonances in Suspended Cables via a Direct Perturbation Approach". In ASME 1997 Design Engineering Technical Conferences. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/detc97/vib-4101.
Testo completoAbstract (sommario):
Abstract We analyze the nonlinear three–dimensional response of an elastic suspended cable with small sag-to-span ratio to a harmonic excitation. We investigate the case of primary resonance of the first in-plane symmetric mode when it is involved in a one–to–one internal resonance with the first antisymmetric planar and nonplanar modes and a two–to–one internal resonance with the first symmetric nonplanar mode. We apply the method of multiple scales directly to the governing two integro–partial–differential equations and associated boundary conditions with no a priori assumption on the shape of the motion. The result is a system of four coupled nonlinear complex–valued equations describing the modulation of the amplitudes and phases of the four interacting modes. The spatial-temporal corrections to the displacement field at higher orders show that the solution is not separable in space and time. Prelimary comparisons with a companion Galerkin-type discretized model show that the latter must be used with some care in studying finite–amplitude motions of cables.
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Salles, Loi¨c, Laurent Blanc, Fabrice Thouverez e Alexander M. Gouskov. "Dynamic Analysis of Fretting-Wear in Friction Contact Interfaces". In ASME Turbo Expo 2008: Power for Land, Sea, and Air. ASMEDC, 2008. http://dx.doi.org/10.1115/gt2008-51112.
Testo completoAbstract (sommario):
Fretting wear is a very important phenomenon occurring in bladed disks. It causes that blades must be replaced in turbomachines during their life-cycle. Methods exist to predict fretting-wear in quasi-static analysis. However they don’t predict all the phenomena observed in blade attachments on real turbomachines. That’s why this study assumes that dynamics plays a role in fretting-wear. This paper is devoted to the realistic modelling and calculation of fretting-wear and dynamical response of structures in unilateral contact with friction. Vibration and wear phenomena present very different scales both in time and space. Therefore the difficulty is in finding methods that enable one to solve the non-linear problem with a good compromise between the approximations made about the dynamical aspects and those linked with fretting-wear issues. Here, phenomenological examples are studied. They involve a small number of degrees of freedom with a view to understanding the complex coupling between vibration and fretting-wear. This way, they will show the relative importance of parameters.
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Roddy, Morgan, Haden Hodges, Larry Roe e Po-Hao Adam Huang. "Demonstration of a Solid-State Inflation Balloon Deorbiter". In ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-71998.
Testo completoAbstract (sommario):
This paper updates on the recent development of the novel Solid State Inflation Balloon (SSIB), a simple, reliable, low-cost, non-propulsive deorbit mechanism for the full range of small satellites, defined by NASA as less than 180 kg. It aims to focus on the recent demonstration, for the first time, inflation of a ∼10 cm sized balloon in a vacuum chamber. Small satellites typically rely on aerodynamic drag to deorbit within the FAA’s 25 year requirements. The SSIB will enhance aerodynamic drag by inflating a balloon at the end-of-life of a satellite mission. This technology will provide a scalable and non-existing capability, low-cost deorbit, for applications in the full-range of smallsats, from CubeSats to MicroSats. The SSIB system is composed of three major components: a Micro-Electro-Mechanical Systems (MEMS) Solid-State Gas Generator (SSGG) chip, a balloon structure made of thin film compatible with space environment (i.e. Mylar, Kapton, or Teflon), and a sub-system package suitable for spacecraft integration. The SSGG is composed of a 2D addressable array of sodium azide (NaN3) crystals, confined by Su-8 wells, on a glass substrate. Current versions include 2×2 and 8×8 arrays designed for a full range of small satellites. Under each well is a resistive heater and when heated to above 350 °C, the NaN3 spontaneously decomposes to generate N2 gas in time scales on the order of 10 milliseconds. Each well is designed with a typical volume of 10–15 m3 to 10−6 m3 of NaN3 (i.e. 1,500 μm × 1,500 μm × 150 μm on the larger end of the spectrum). The SSIB system is low power (∼1 W per well for less than 10 seconds) and have low mass (∼100 grams, where mass is dominated by the size of the required balloon). Initial simulations have shown that the SSIB with balloons of 1 m2 cross-section can deorbit small satellites from above 1000 km well within 25 years.
Rapporti di organizzazioni sul tema "Small space-Time scales"
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Hughes, Ceri, Miguel Martinez Lucio, Stephen Mustchin e Miriam Tenquist. Understanding whether local employment charters could support fairer employment practices: Research Briefing Note. University of Manchester Work and Equalities Institute, maggio 2024. http://dx.doi.org/10.3927/uom.5176698.
Testo completoAbstract (sommario):
Employment charters are voluntary initiatives that attempt to describe ‘good’ employment practices and to engage and recognise those employers that meet or aspire to meet these practices. They can operate at different spatial scales, ranging from international and national accreditation schemes to local charters that focus on engaging employers in specific regions or cities. The latter are the focus of this briefing paper. At least six city-regions in England had local employment charters at the time of our research. These areas alone account for over a fifth (21 per cent) of the resident working-age population (based on ONS 2022 population estimates), highlighting the potential reach and significance of these voluntary initiatives in terms of setting employment standards, although the number of employers directly accredited with local schemes is still relatively small. Despite their popularity with policymakers, there is only limited research on local employment charters. A few studies have explored issues relating to the design, implementation and evaluation of charters, reflecting demand from policymakers for toolkits and support to develop local policy initiatives (e.g. Crozier, 2022). But several years into the implementation of some of these charter initiatives, and as more areas look to develop their own, we argue that it is time to revisit some more foundational questions around what local charters are for, and how far they can support ‘good work’ agendas. It remains to be seen which employers can and will engage substantively with these initiatives, how employer commitments might be validated and the good employment criteria enforced, and how local charters will be integrated with local authority commissioning and procurement practices (TUC, 2022). The local charters that have emerged so far within the UK have been conceived predominantly as employer engagement tools, adopting language and approaches designed to appeal to employer interests and priorities and emphasising the value that employers can derive from being part of the initiative. This contrasts with approaches emphasising the engagement of other constituents, like citizens and employees, as a route to influencing employer engagement (Scott, Baylor and Spaulding, 2016; Johnson, Herman and Hughes, 2022). This briefing paper shares findings from a scoping study involving key informants in the North West of England (2022-2023) which explored how local charter initiatives could influence employers to improve their employment practices. Participants in the study shared their views on: 1) How voluntary local employment charters could influence employers to change their employment practices? 2) What types of employers local charters could engage and influence? Alongside this study, we have also developed a series of case studies of the charters that have been introduced across six city regions in England. These encompass the Fair Work Standard (London); Good Employment Charter (West of England); Good Work Pledge (North of Tyne Combined Authority); Fair Employment Charter (Liverpool City Region Combined Authority); Good Employment Charter (Greater Manchester) and the Fair Work Charter (West Yorkshire Combined Authority). The case studies are published separately. Our conversations with policymakers, union representatives and campaigners indicate that while there are some potential ‘win-win’ outcomes from promoting good employment practices, there are also some key tensions that should be more clearly acknowledged. In particular, one point of divergence relates to what would be the most effective and meaningful way to engage with employers in order to secure improvements in employment practices. On the one hand, employment charter initiatives could set consistent, clear and relatively high standards of practice that employers could be required to meet from the outset, creating a clear dividing line between those employers who were engaged in some way with the initiative and those who are not. On the other, these initiatives could prioritise engaging as many employers as possible with few or no specific red lines (e.g. around paying the living wage) so that the charter provides an opportunity to work with employers to secure hopefully more substantive commitments down the road. There are challenges and trade-offs associated with both of these viewpoints. One problem with the former strategy of setting a consistent standard is that the principles of employment that the charter promotes may not be particularly stretching in some sectors, or indeed may only describe a minimum set of commitments for certain types of work; whilst in other sectors they may be viewed as being too stringent. A more incremental, flexible strategy of engaging with employers and working with them to change their employment practices, in contrast, relies on sustained commitment from both policymakers and employers. Whether charters can simultaneously offer a ‘safe space’ to employers to share information and change their practices whilst also operating in a more regulatory way appears as a fundamental tension in existing visions for these initiatives. We return to these different views on how to engage employers and secure change in the conclusion to this paper.