Search results for " gravity"
showing 10 items of 267 documents
GW170817: Implications for the Stochastic Gravitational-Wave Background from Compact Binary Coalescences
2018
The LIGO Scientific and Virgo Collaborations have announced the first detection of gravitational waves from the coalescence of two neutron stars. The merger rate of binary neutron stars estimated from this event suggests that distant, unresolvable binary neutron stars create a significant astrophysical stochastic gravitational-wave background. The binary neutron star background will add to the background from binary black holes, increasing the amplitude of the total astrophysical background relative to previous expectations. In the Advanced LIGO-Virgo frequency band most sensitive to stochastic backgrounds (near 25 Hz), we predict a total astrophysical background with amplitude $\Omega_{\rm…
Improving operational performance in altered gravity
2022
Human motor adaptation is crucial to remain efficient when exposed to unfamiliar environments. In these contexts, the efficient strategies developed by the brain to optimise movement can prove deficient. Dexterous manual movement execution in space therefore require the learning of new coordinated motor actions. Traditionally, adaptation mechanisms are tested in laboratory using robotic devices that disturb the limb specifically involved in the task while the dynamics of the rest of the body remain unchanged. Although participants build a more accurate representation of the task over repetitions, these approaches are limiting as they do not reflect the ecological adjustment to globally modi…
Conformal transformations and weak field limit of scalar-tensor gravity
2013
The weak field limit of scalar tensor theories of gravity is discussed in view of conformal transformations. Specifically, we consider how physical quantities, like gravitational potentials derived in the Newtonian approximation for the same scalar-tensor theory, behave in the Jordan and in the Einstein frame. The approach allows to discriminate features that are invariant under conformal transformations and gives contributions in the debate of selecting the true physical frame. As a particular example, the case of $f(R)$ gravity is considered.
Trade Costs, Trade Balances, and Current Accounts: an application of Gravity to Multilateral Trade
2005
In this paper we test the well-known hypothesis of Obstfeld and Rogoff (NBER Macroeconomics Annual 7777:339–390, 2000) that trade costs are the key to explaining the so-called Feldstein–Horioka puzzle. Our approach has a number of novel features. First, we focus on the interrelationship between trade costs, the trade account and the Feldstein–Horioka puzzle. Second, we use the gravity model to estimate the effect of trade costs on bilateral trade and, third, we show how bilateral trade can be used to draw inferences about desired trade balances and desired intertemporal trade. Our econometric results provide strong support for the Obstfeld and Rogoff hypothesis and we are also able to recon…
Regional inequalities as drivers of affective polarization
2022
This paper investigates divergences in levels of affective polarization across Belgian regions around the 2019 elections. Elaborating on the relative deprivation theory, we analyse the role of current and long-term socio-economic regional inequalities and of geographical distance separating regions. Empirically, we aggregate individual-level measures of affective polarization at the Belgian NUTS-3 level and use a gravity approach to explore the determinants of regional divergences. Our results show that regional variations in affective polarization are best explained by a current rural–urban divide and by how regions have performed economically in the last years. We also show that geographi…
International trade and migrant networks: Is It really about qualifications?
2014
Personal characteristics of migrants could help to strengthen the impact of migrant networks on bilateral trade. While most of the attention has been focused on immigrants' educational attainment, this paper focuses on the relevance of the tasks carried out by migrants. Our empirical results confirm that the existence of a large number of foreign-born workers with managerial duties is critical to explain the reduction of transaction costs caused by migrant networks.
Semiclassical geons as solitonic black hole remnants
2013
We find that the end state of black hole evaporation could be represented by non-singular and without event horizon stable solitonic remnants with masses of the order the Planck scale and up to similar to 16 units of charge. Though these objects are locally indistinguishable from spherically symmetric, massive electric (or magnetic) charges, they turn out to be sourceless geons containing a wormhole generated by the electromagnetic field. Our results are obtained by interpreting semiclassical corrections to Einstein's theory in the first-order (Palatini) formalism, which yields second-order equations and avoids the instabilities of the usual (metric) formulation of quadratic gravity. We als…
A deep study of the high–energy transient sky
2021
This is an open access article. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds t…
Robust Redundant Input Reliable Tracking Control for Omnidirectional Rehabilitative Training Walker
2014
Published version of an article in the journal: Mathematical Problems in Engineering. Also available from the publisher at: http://dx.doi.org/10.1155/2014/636934 The problem of robust reliable tracking control on the omnidirectional rehabilitative training walker is examined. The new nonlinear redundant input method is proposed when one wheel actuator fault occurs. The aim of the study is to design an asymptotically stable controller that can guarantee the safety of the user and ensure tracking on a training path planned by a physical therapist. The redundant degrees of freedom safety control and the asymptotically zero state detectable concept of the walker are presented, the model of redu…
Adaptive neural-fuzzy inference system based method to modeling of vehicle crash
2013
Various areas of research need to be considered in order to establish a mathematical model of a vehicle crash. To enhance the modeling process, a novel ANFIS-based approach to reconstruct behavior of impacting vehicles is presented in this paper. Kinematics of center of gravity (COG) a vehicle involved in an oblique barrier collision is reproduced by application of a five-layered ANFIS structure. Then, the same ANFIS system is used to simulate a different collision type than the one which was used in the training stage. The points of interests are selected to be the locations of accelerometers mounting. The accuracy of the proposed method is evaluated by the comparative analysis with the re…