2,293 research outputs found
Job Selection in a Network of Autonomous UAVs for Delivery of Goods
This article analyzes two classes of job selection policies that control how
a network of autonomous aerial vehicles delivers goods from depots to
customers. Customer requests (jobs) occur according to a spatio-temporal
stochastic process not known by the system. If job selection uses a policy in
which the first job (FJ) is served first, the system may collapse to
instability by removing just one vehicle. Policies that serve the nearest job
(NJ) first show such threshold behavior only in some settings and can be
implemented in a distributed manner. The timing of job selection has
significant impact on delivery time and stability for NJ while it has no impact
for FJ. Based on these findings we introduce a methodological approach for
decision-making support to set up and operate such a system, taking into
account the trade-off between monetary cost and service quality. In particular,
we compute a lower bound for the infrastructure expenditure required to achieve
a certain expected delivery time. The approach includes three time horizons:
long-term decisions on the number of depots to deploy in the service area,
mid-term decisions on the number of vehicles to use, and short-term decisions
on the policy to operate the vehicles
Connectivity of the Outer Plexiform Layer of the Mouse Retina
The retina has two synaptic layers: In the outer plexiform layer (OPL), signals from the
photoreceptors (PRs) are relayed to the bipolar cells (BCs) with one type of horizontal
cell (HC) as interneuron. In the inner plexiform layer (IPL), the retinal ganglion cells
(RGCs) receive input from the bipolar cells, modulated by multiple types of amacrine
cells. The axons of the retinal ganglion cells form the optic nerve which transmit the
visual signal to the higher regions of the brain (Masland 2012).
Studies of signal processing in the retina usually focus on the inner plexiform layer.
Here, the main computations take place such as direction selectivity, orientation selectivity
and object motion detection (Gollisch and Meister 2010). However, to fully
understand how these computations arise, it is also important to understand how the
input to the ganglion cells is computed and thus to understand the functional differences
between BC signals. While these are shaped to some extent in the IPL through amacrine
cell feedback (Franke et al. 2017), they are also influenced by computations in the OPL
(Drinnenberg et al. 2018). Accordingly, it is essential to understand how the bipolar cell
signals are formed and what the exact connectivity in the OPL is.
This thesis project aims at a quantitative picture of the mouse outer retina connectome.
It takes the approach of systematically analyzing connectivity between the cell types
in the OPL based on available high-resolution 3D electron microscopy imaging data
(Helmstaedter et al. 2013). We reconstructed photoreceptor axon terminals, horizontal
cells and bipolar cells, and quantified their contact statistics. We identified a new
structure on HC dendrites which likely defines a second synaptic layer in the OPL
below the PRs. Based on the reconstructed morphology, we created a biophysical model
of a HC dendrite to gain insights into potential functional mechanisms.
Our results reveal several new connectivity patterns in the mouse OPL and suggest
that HCs perform two functional roles at two distinct output sites at the same time.
The project emphasizes how large-scale EM data can boost research on anatomical
connectivity and beyond and highlights the value of the resulting data for detailed
biophysical modeling. Moreover, it shows how the known amount of complexity
increases with the level of detail with which we can study a subject. Beyond that, this
thesis project demonstrates the benefits of data sharing and open science which only
enabled our studies
Signatures of criticality arise in simple neural population models with correlations
Large-scale recordings of neuronal activity make it possible to gain insights
into the collective activity of neural ensembles. It has been hypothesized that
neural populations might be optimized to operate at a 'thermodynamic critical
point', and that this property has implications for information processing.
Support for this notion has come from a series of studies which identified
statistical signatures of criticality in the ensemble activity of retinal
ganglion cells. What are the underlying mechanisms that give rise to these
observations? Here we show that signatures of criticality arise even in simple
feed-forward models of retinal population activity. In particular, they occur
whenever neural population data exhibits correlations, and is randomly
sub-sampled during data analysis. These results show that signatures of
criticality are not necessarily indicative of an optimized coding strategy, and
challenge the utility of analysis approaches based on equilibrium
thermodynamics for understanding partially observed biological systems.Comment: 36 pages, LaTeX; added journal reference on page 1, added link to
code repositor
A Roadmap to Enhanced Regional Energy Policy: Cooperation in South East Europe. CEPS Special Report, No. 134/April 2016
Regional Energy Policy Cooperation has now gained political traction in the EU as a tool to advance the EU’s energy objectives. Cooperation and coordination is meant to facilitate the convergence of markets and policies, so while the creation of one EU Internal Energy Market remains the goal, regional cooperation is the tool with which to achieve that goal. Cooperation could become the stepping-stone towards the completion of the Internal Energy Market within the European 2030 climate and energy framework and beyond
Toward an Aesthetics of Adaptation in Empirical Research
In their article Toward an Aesthetics of Adaptation in Empirical Research Marion Behrens, Christian Kell, and Pascal Nicklas discuss the requirements and potential of empirical research into the reception of adaptations: adaptation is one key strategy in the creation of literature and art in general. The creative process and product of adaptation has its counter-part on the side of reception. Empirical research into the aesthetics of adaptation aims at the experimental elucidation of the physiological background and the establishment of a model describing the perceptual underpinnings of the act of seeing an adaptation as adaptation. This implies evolutionary biological reasoning concerning the memory tasks required for this kind of perception and experimental work showing neuronal, psychological and perceptual specificities contrasting acts of reception of artistic and non-artistic stimuli. A particularly promising arena for model building research lies in poetic language and rhetorical structures of repetition
RDA in Germania, Austria e nella Svizzera tedesca: un nuovo standard non solo per le biblioteche
La comunità bibliotecaria in Germania, Austria e nella Svizzera tedesca ha raggiunto alla fine del 2015 un obiettivo comune. Dopo due anni di intensa preparazione, lo standard internazionale RDA è stato implementato e si è avviato il lavoro pratico.L'articolo descrive il progetto dal punto di vista della situazione organizzativa nei tre paesi e si concentra sugli obiettivi raggiunti e sul lavoro che resta ancora da fare.Offre inoltre una panoramica dell'impegno iniziale per allineare la gestione dei materiali speciali con RDA nelle nazioni di lingua tedesca e descrive le attività associate al requisito specifico derivante dalla natura multilingue della Svizzera. Infine, l'articolo riferisce lo sviluppo strategico nei comitati internazionali RDA, come il RDA Steering Committee (RSC) e l'European RDA Interest Group (EURIG).The library community in Germany, Austria and German-speaking Switzerland achieved a common goal at the end of 2015. After more than two years of intensive preparation, the international standard RDA was implemented and the practical work has now started. The article describes the project in terms of the political and organizational situation in the three countries, and points out the objectives which have been achieved as well as the work which is still outstanding. An overview is given of the initial efforts to align special materials with RDA in the German-speaking countries, and the tasks associated with the specific requirements arising from the multilingual nature of Switzerland are described. Furthermore, the article reports on the current strategic developments in the international RDA committees like the RDA Steering Committee (RSC) and the European RDA Interest Group (EURIG)
On modelling of shear fracture in deep drawing of a high-strength dual-phase sheet steel
The paper presents application of fracture behaviour characterisation results of a dual-phase sheet steel DP600 to an FEA of its deep-drawing for shear fracture prediction. The characterisation results were obtained with the help of a characterisation method based on a tensile test on a novel butterfly specimen and published previously by the authors. The aim of the present paper is to evaluate that characterisation method on a deep-drawing process. Based on the previous results of the authors, the fracture behaviour is modelled here with the help of the modified Mohr-Coloumb fracture model. The obtained FEA results reveal that shear fracture of the studied material is predicted too early by the used MMC fracture model. A novel adjustment of the model is proposed yielding infinitely high fracture strains at strongly pressure-superimposed stress states. As it is often the case in the state-of-the-art fracture characterisation of high-strenght sheet steels, such stress states were not tested during the previously performed fracture characterisation but occur during the studied deep drawing process. With the help of the adjusted MMC fracture model, it is possible to predict the crack initiation moment very accurately and the crack initiation location sufficiently accurately. © Published under licence by IOP Publishing Ltd
Influences on the formability and mechanical properties of 7000-aluminum alloys in hot and warm forming
Aluminum alloys of the 7000 series possess high lightweight potential due to their high specific tensile strength combined with a good ultimate elongation. For this reason, hot-formed boron-manganese-steel parts can be substituted by these alloys. Therefore, the application of these aluminum alloys for structural car body components is desired to decrease the weight of the body in white and consequently CO2 emissions during vehicle operation. These days, the limited formability at room temperature limits an application in the automobile industry. By increasing the deformation temperature, formability can be improved. In this study, two different approaches to increase the formability of these alloys by means of higher temperatures were investigated. The first approach is a warm forming route to form sheets in T6 temper state with high tensile strength at temperatures between 150 °C and 300 °C. The second approach is a hot forming route. Here, the material is annealed at solution heat treatment temperature and formed directly after the annealing step. Additionally, a quench step is included in the forming stage. After the forming and quenching step, the sheets have to be artificially aged to achieve the high specific tensile strength. In this study, several parameters in the presented process routes, which influence the formability and the mechanical properties, have been investigated for the aluminum alloys EN AW7022 and EN AW7075. © Published under licence by IOP Publishing Ltd
Europe's LNG Strategy in the Wider EU Gas Market. CEPS Policy Brief No. 333, October 2015
In its Communication on an Energy Union published in February 2015, the European Commission committed itself to “explore the full potential of liquefied natural gas (LNG), including as a back-up in crisis situations when insufficient gas is coming into Europe through the existing pipeline system” and to address the potential of gas storage in Europe by developing a comprehensive LNG and storage strategy by the end of 2015 or early in 2016.
This is a comprehensible move in the current context. Geopolitical tensions between the EU and Russia explain the EU’s willingness to further diversify its supply sources of natural gas to reinforce its long-term energy security on the one hand, and to strengthen its ability to solve future crises on the other hand. Moreover, the current market dynamics could support diversification towards LNG. Increasing the flexibility of LNG trade, decreasing LNG prices and LNG charter rates and an apparent price convergence between the European and the Asia-Pacific LNG imports would all reinforce the economic viability of such a strategy.
This Policy Brief makes three main points:
• For the LNG and gas storage strategy to work, it needs to be embedded in the realities of the natural gas market.
• The key to a successful LNG strategy is to develop sufficient infrastructure.
• The LNG strategy needs an innovation component
Experimental Characterization and Material Modelling of an AZ31 Magnesium Sheet Alloy at Elevated Temperatures under Consideration of the Tension-Compression Asymmetry
Magnesium sheet alloys have a great potential as a construction material in the aerospace and automotive industry. However, the current state of research regarding temperature dependent material parameters for the description of the plastic behaviour of magnesium sheet alloys is scarce in literature and accurate statements concerning yield criteria and appropriate characterization tests to describe the plastic behaviour of a magnesium sheet alloy at elevated temperatures in deep drawing processes are to define. Hence, in this paper the plastic behaviour of the well-established magnesium sheet alloy AZ31 has been characterized by means of convenient mechanical tests (e. g. tension, compression and biaxial tests) at temperatures between 180 and 230 °C. In this manner, anisotropic and hardening behaviour as well as differences between the tension-compression asymmetry of the yield locus have been estimated. Furthermore, using the evaluated data from the above mentioned tests, two different yield criteria have been parametrized; the commonly used Hill'48 and an orthotropic yield criterion, CPB2006, which was developed especially for materials with hexagonal close packed lattice structure and is able to describe an asymmetrical yielding behaviour regarding tensile and compressive stress states. Numerical simulations have been finally carried out with both yield functions in order to assess the accuracy of the material models
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