849 research outputs found
Katalog der Musikbibliothek Peters ...
No full textClassified, with author indexes.Preface signed: C.F. Peters. Dr. Emil Vogel, bibliothekar.Abth. 1. Theoretische Werke.--Abth. 2. Praktische Werke.Mode of access: Internet
The dynamics of financial instability: simplifying Keen’s Goodwin–Minsky model
Get PDFMarket capitalism typically goes through cycles of expansion and contraction. Every now and then, these common economic cycles go off the hinges. They become unstable and can lead to recessions, crises and depressions—phenomena that economists typically explain by looking to exogenous forces. Alternative explanations—mostly Marxian and Keynesian—for the instabilities have been sought within the structure of the economic system itself. One such explanation is provided by Steve Keen in his Goodwin–Minsky model. The model effectively mimics the dynamics of key indicators prior to, during and after the 2007/08 crisis. However, the model is also over‐specified, highly sensitive to initial conditions and therefore more difficult to convey. In line with George Box's plea for parsimony, this paper presents a more straightforward version of Keen's model that remains consistent with its fundamental behaviour. The model also illustrates the potential for further dialogue between Marxian economics and system dynamics
Motion of quantum vortex lines near realistic rough boundaries
No full textWe numerically solve the three--dimensional, time--dependent Gross--Pitaevskii equation to model a superfluid flowing over a realistic rough boundary. Our model for the boundary is based on the atom--force microscope image of a NbTi vibrating wire used to generate turbulence in actual experiments. We find that near the boundary a dense region of quantum vortices is created, which forms a kind of `superfluid boundary layer'
Wave excitations in adjacent vortex filaments
No full textThe interactions of the nearest neighbour vortices are argued to play a significant role in the crossover range of scales that lies between the Kolmogorov-Richardson cascade and the Kelvin wave driven cascade in superfluid turbulence. In this work, we study how a wave excitation (a Kelvin wave or a soliton) on a vortex affects a nearby straight vortex. Our numerical simulations reveal that coherent excitations can hop from one vortex filament to another whilst retaining their coherent properties
Spectral properties of Andreev reflection from quantum turbulence in 3He-B: What do they tell about turbulent fluctuations?
No full textOne of the experimental techniques developed to measure quantum turbulence at low temperatures in 3He-B utilizes the Andreev reflection of thermal quasiparticle excitations from quantized vortices and vortex structures. We present the results of theoretical, numerical, and experimental study of Andreev scattering from quantum turbulence in 3He-B. We analyze the spectral properties of the Andreev reflection and compare these with the spectral properties of superfluid turbulence, and discuss the physical mechanisms responsible for the scaling of spectral densities. Finally, we discuss the relation between our findings and related observables in ordinary turbulence
The impact of COVID-19 on the eradication of poverty: an incorrect diagnosis
No full textThe COVID-19 pandemic is said to have reversed a decade of progress towards poverty alleviation. This opinion piece contends that this diagnosis is incomplete and possibly incorrect. It distracts us from understanding the ways in which the impacts of the pandemic are embedded in a longer trajectory of unjust economic development. Two problems are highlighted: a more reasonable international poverty line shows that extreme poverty is on the rise, and the alleged progress fails to account for relatively fast-rising food prices. COVID-19 is therefore not reversing any meaningful trend; it is merely aggravating the problem. Ignoring this critique, the inclusive growth and productive employment agendas persist in their aim to incorporate the poor in an economic system that – compelled by its own logic – (re)produces poverty, inequality and hunger and undermines welfare. Simply reinforcing these agendas in light of COVID-19 bypasses the question of the desirability and viability of the system in which the poor are supposed to be incorporated
Tracing the Causal Loops Through Local Perceptions of Rural Road Impacts in Ethiopia
No full textTo better grasp the interconnected range of socioeconomic impacts from the implementation of rural roads in northern Ethiopia, we have experimented with Causal Loop Diagrams (CLDs), a tool commonly used in systems dynamics, but generally under-used in development research. The expansion of the rural road network in Africa is praised for reducing spatial isolation, lowering transport cost, increasing access to markets, and bringing services closer to home. However, different segments of society will benefit differently from the establishment of a rural road. This difference may lead to dynamics that either exacerbate or reduce existing inequities, which forms the central question for this paper. As part of a broader study on the multiple (in)direct effects of rural roads on productive employment, we undertook oral testimonies in four municipalities to explore how people perceive road impacts on livelihoods, mobility, and work. CLDs were then used to assemble those seemingly loose observations into a systematized view of the whole. The exercise reveals conflicting feedback processes that may dominate system at different times and drive the inequities between surplus food producers and laborer households up or down. The method used can be particularly useful for studying similar infrastructures that seemingly bring benefits to all, but may cause subtle, concealed or delayed effects, and ultimately surprising system behavior
A systems and thermodynamics perspective on technology in the circular economy
Get PDFSeveral discourses on environment and sustainability are characterised by a strong confidence in the potential of technology to address, if not solve, the ecological impacts resulting from physically expanding systems of production and consumption. The optimism is further encouraged by leading environmental engineering concepts, including cradle-to-cradle and industrial ecology, as well as broader frameworks, such as natural capitalism and the circular economy. This paper explores the viability of their promise from a biophysical perspective, which is based on insights from system dynamics and thermodynamics. Such an ecological reality check is generally ignored or underestimated in the literature on aforementioned concepts and frameworks. The paper ultimately reflects on what role society can realistically assign to technology for resolving its ecological concerns. While environmental engineering undoubtedly has something to offer, it will end up chasing its tail if the social and economic forces driving up production and consumption are not addressed
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