10,217 research outputs found
A six-part collisional model of the main asteroid belt
In this work, we construct a new model for the collisional evolution of the
main asteroid belt. Our goals are to test the scaling law of Benz and Asphaug
(1999) and ascertain if it can be used for the whole belt. We want to find
initial size-frequency distributions (SFDs) for the considered six parts of the
belt (inner, middle, 'pristine', outer, Cybele zone, high-inclination region)
and to verify if the number of synthetic asteroid families created during the
simulation matches the number of observed families as well. We used new
observational data from the WISE satellite (Masiero et al., 2011) to construct
the observed SFDs. We simulate mutual collisions of asteroids with a modified
version of the Boulder code (Morbidelli et al., 2009), where the results of
hydrodynamic (SPH) simulations of Durda et al. (2007) and Benavidez et al.
(2012) are included. Because material characteristics can significantly affect
breakups, we created two models - for monolithic asteroids and for
rubble-piles. To explain the observed SFDs in the size range D = 1 to 10 km we
have to also account for dynamical depletion due to the Yarkovsky effect. The
assumption of (purely) rubble-pile asteroids leads to a significantly worse fit
to the observed data, so that we can conclude that majority of main-belt
asteroids are rather monolithic. Our work may also serve as a motivation for
further SPH simulations of disruptions of smaller targets (with a parent body
size of the order of 1 km).Comment: Accepted for publication in Icaru
GResilient index to assess the greenness and resilience of the automotive supply chain
Purpose: The purpose of this paper is to suggest an Index entitled GResilient Index to assess the greenness and resilience of the automotive companies and corresponding supply chain. Design/methodology/approach: An integrated assessment model is proposed based on Green and Resilient practices. These practices are weighted according to their importance to the automotive supply chain competitiveness. The Delphi technique is used to obtain the weights for the focused supply chain paradigms and corresponding practices. The model is then tested using a case study approach in the automotive supply chain. Findings: The case study results confirmed the applicability of this Index in a real-world supply chain. The results show that the Resilient supply chain management paradigm is the one considered as the one that more contributes for the automotive supply chain competitiveness. Research limitations/implications: The proposed Index was developed in the automotive sector context therefore it could not be adjusted to a different one. Future research could consider other aggregation methods for the Index construction. Practical implications: Supply chain participants will be able to evaluate the performance of their companies or supply chain in terms of Green and Resilient paradigms. Also, the Index can be effectively employed for functional benchmarking among competing companies and supply chains.Green; resilient; supply chain management; index; automotive industry
Brazilian biofuels policies and impacts on world agricultural trade
Agricultural and Food Policy, Resource /Energy Economics and Policy,
Non universality of entanglement convertibility
Recently, it has been suggested that operational properties connected to
quantum computation can be alternative indicators of quantum phase transitions.
In this work we systematically study these operational properties in 1D systems
that present phase transitions of different orders. For this purpose, we
evaluate the local convertibility between bipartite ground states. Our results
suggest that the operational properties, related to non-analyticities of the
entanglement spectrum, are good detectors of explicit symmetries of the model,
but not necessarily of phase transitions. We also show that thermodynamically
equivalent phases, such as Luttinger liquids, may display different
convertibility properties depending on the underlying microscopic model.Comment: 5 pages + references, 4 figures - improved versio
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Oxygen/Glucose deprivation induces a reduction in synaptic AMPA receptors on hippocampal CA3 neurons mediated by mGluR1 and adenosine A3 receptors
Hippocampal CA1 pyramidal neurons are highly sensitive to ischemic damage, whereas neighboring CA3 pyramidal neurons are less susceptible. It is proposed that switching of AMPA receptor (AMPAR) subunits on CA1 neurons during an in vitro model of ischemia, oxygen/glucose deprivation (OGD), leads to an enhanced permeability of AMPARs to Ca2+, resulting in delayed cell death. However, it is unclear whether the same mechanisms exist in CA3 neurons and whether this underlies the differential sensitivity to ischemia. Here, we investigated the consequences of OGD for AMPAR function in CA3 neurons using electrophysiological recordings in rat hippocampal slices. Following a 15 min OGD protocol, a substantial depression of AMPAR-mediated synaptic transmission was observed at CA3 associational/commissural and mossy fiber synapses but not CA1 Schaffer collateral synapses. The depression of synaptic transmission following OGD was prevented by metabotropic glutamate receptor 1 (mGluR1) or A3 receptor antagonists, indicating a role for both glutamate and adenosine release. Inhibition of PLC, PKC, or chelation of intracellular Ca2+ also prevented the depression of synaptic transmission. Inclusion of peptides to interrupt the interaction between GluA2 and PICK1 or dynamin and amphiphysin prevented the depression of transmission, suggesting a dynamin and PICK1-dependent internalization of AMPARs after OGD. We also show that a reduction in surface and total AMPAR protein levels after OGD was prevented by mGluR1 or A3 receptor antagonists, indicating that AMPARs are degraded following internalization. Thus, we describe a novel mechanism for the removal of AMPARs in CA3 pyramidal neurons following OGD that has the potential to reduce excitotoxicity and promote neuroprotectio
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