Semiclassical and Stochastic Gravity

Author(s):  
Bei-Lok B. Hu ◽  
Enric Verdaguer
Keyword(s):  
2017 ◽  
Vol 13 (4) ◽  
pp. 192 ◽  
Author(s):  
Hai Thi Hong Nguyen ◽  
Thang Ngoc Doan

This study employs a stochastic gravity model to estimate the efficiency performance of Vietnam’s trade with its main trading partners from 1995-2015. Trade efficiency is measured as the ratio of actual trade volume to the maximum likelihood. Moreover. it analyzes the effects of both natural and man-made trade barriers on trade efficiency. The empirical results suggest that the actual trade of Vietnam appears to be much smaller than a possible efficiency level and that there is large space for further progress. Export efficiency outweighs that of import. Vietnam’s ASEAN Free Trade Agreement membership has, in general, improved the trade efficiency, whereas tariffs and domestic devaluation have impaired it. Our findings lead to the recommendation that Vietnam should join more Free Trade Agreements and break down the man-made barriers.


Geophysics ◽  
2013 ◽  
Vol 78 (2) ◽  
pp. G15-G24 ◽  
Author(s):  
Pejman Shamsipour ◽  
Denis Marcotte ◽  
Michel Chouteau ◽  
Martine Rivest ◽  
Abderrezak Bouchedda

The flexibility of geostatistical inversions in geophysics is limited by the use of stationary covariances, which, implicitly and mostly for mathematical convenience, assumes statistical homogeneity of the studied field. For fields showing sharp contrasts due, for example, to faults or folds, an approach based on the use of nonstationary covariances for cokriging inversion was developed. The approach was tested on two synthetic cases and one real data set. Inversion results based on the nonstationary covariance were compared to the results from the stationary covariance for two synthetic models. The nonstationary covariance better recovered the known synthetic models. With the real data set, the nonstationary assumption resulted in a better match with the known surface geology.


Author(s):  
Thomas C Andersen

Some physicists surmise that gravity lies outside of quantum mechanics. Thus theories like the standard semiclassical theory of quantum to gravity coupling (that of Rosenfeld and Møller) are possible real models of interaction, rather than a mere approximation of a theory of quantum gravity. Unfortunately, semiclassical gravity creates inconsistencies such as superluminal communication. Alternatives by authors such as Diósi, Martin, Penrose, and Wang often use the term 'stochastic' to set themselves apart from the standard semiclassical theory. These theories couple to fluctuations caused by for instance continuous spontaneous localization, hence the term 'stochastic'. This paper looks at stochastic gravity in the framework of a class of emergent or ontological quantum theories, such as those by Bohm, Cetto, and de Broglie. It is found that much or all of the trouble in connecting gravity with a microscopic system falls away, as Einstein's general relativity is free to react directly with the microscopic beables. The resulting continuous gravitational wave radiation by atomic and nuclear systems does not, in contrast to Einstein's speculation, cause catastrophic problems. The small amount of energy exchanged by gravitational waves may have measurable experimental consequences. A very recent experiment by Vinante et al. performed on a small cantilever at mK temperatures shows a surprising non-thermal noise component, the magnitude of which is consistent with the stochastic gravity coupling explored here.


2004 ◽  
Vol 7 (1) ◽  
Author(s):  
Bei Lok Hu ◽  
Enric Verdaguer

2017 ◽  
Vol 18 (2) ◽  
pp. 276-295 ◽  
Author(s):  
Tina Barma

This article is an empirical study employing various time-invariant and time-varying specifications of a stochastic gravity model of trade. It enumerates the inefficiency component among the determinants of Indian agricultural export flows to 112 partner countries, over the years 2000–2013. The panel study finds empirical support for high yet decreasing home country inefficiency or ‘behind-the-border’ constraints to trade. Also significance of regional groups ASEAN, SAFTA and Africa shows that trade policy concentrating on developing countries have been successful export policies. Thus, the export efficiency scores help in articulating future policy initiatives for diversification of the country’s exports according to the significance and level of efficiency of partners. Nevertheless, literal interpretations of the efficiency scores are sensitive to the nature of modelling and their specifications.


2017 ◽  
Vol 141 (5) ◽  
pp. 3628-3628
Author(s):  
Christophe MILLET ◽  
Bruno RIBSTEIN ◽  
Francois LOTT

2020 ◽  
Vol 7 (5) ◽  
pp. 191858
Author(s):  
S. M. Fischer ◽  
M. Beck ◽  
L.-M. Herborg ◽  
M. A. Lewis

Human traffic along roads can be a major vector for infectious diseases and invasive species. Though most road traffic is local, a small number of long-distance trips can suffice to move an invasion or disease front forward. Therefore, understanding how many agents travel over long distances and which routes they choose is key to successful management of diseases and invasions. Stochastic gravity models have been used to estimate the distribution of trips between origins and destinations of agents. However, in large-scale systems, it is hard to collect the data required to fit these models, as the number of long-distance travellers is small, and origins and destinations can have multiple access points. Therefore, gravity models often provide only relative measures of the agent flow. Furthermore, gravity models yield no insights into which roads agents use. We resolve these issues by combining a stochastic gravity model with a stochastic route choice model. Our hybrid model can be fitted to survey data collected at roads that are used by many long-distance travellers. This decreases the sampling effort, allows us to obtain absolute predictions of both vector pressure and pathways, and permits rigorous model validation. After introducing our approach in general terms, we demonstrate its benefits by applying it to the potential invasion of zebra and quagga mussels ( Dreissena spp.) to the Canadian province British Columbia. The model yields an R 2 -value of 0.73 for variance-corrected agent counts at survey locations.


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