Causal hierarchy in modified gravity

We investigate the causal hierarchy in various modified theories of gravity. In general relativity the standard causal hierarchy, (key elements of which are chronology, causality, strong causality, stable causality, and global hyperbolicity), is well-established. In modified theories of gravity there is typically considerable extra structure, (such as: multiple metrics, aether fields, modified dispersion relations, Hořava-like gravity, parabolic propagation, etcetera), requiring a reassessment and rephrasing of the usual causal hierarchy. We shall show that in this extended framework suitable causal hierarchies can indeed be established, and discuss the implications for the interplay between “superluminal” propagation and causality. The key distinguishing feature is whether the signal velocity is finite or infinite. Preserving even minimal notions of causality in the presence of infinite signal velocity requires the aether field to be both unique and hypersurface orthogonal, leading us to introduce the notion of global parabolicity.

Emerging orthobunyaviruses associated with CNS disease

The Orthobunyavirus genus comprises a wide range of arthropod-borne viruses which are prevalent worldwide and commonly associated with central nervous system (CNS) disease in humans and other vertebrates. Several orthobunyaviruses have recently emerged and increasingly more will likely do so in the future. Despite this large number, an overview of these viruses is currently lacking, making it challenging to determine importance from a One Health perspective. Causality is a key feature of determining importance, yet classical tools are unfit to evaluate the causality of orthobunyaviral CNS disease. Therefore, we aimed to provide an overview of orthobunyaviral CNS disease in vertebrates and objectify the causality strength of each virus. In total, we identified 27 orthobunyaviruses described in literature to be associated with CNS disease. Ten were associated with disease in multiple host species of which seven included humans. Seven viruses were associated with both congenital and postnatal CNS disease. CNS disease-associated orthobunyaviruses were spread across all known Orthobunyavirus serogroups by phylogenetic analyses. Taken together, these results indicate that orthobunyaviruses may have a common tendency to infect the CNS of vertebrates. Next, we developed six tailor-made causality indicators and evaluated the causality strength of each of the identified orthobunyaviruses. Nine viruses had a ‘strong’ causality score and were deemed causal. Eight had a ‘moderate’ and ten a ‘weak’ causality score. Notably, there was a lack of case-control studies, which was only available for one virus. We, therefore, stress the importance of proper case-control studies as a fundamental aspect of proving causality. This comprehensible overview can be used to identify orthobunyaviruses which may be considered causal, reveal research gaps for viruses with moderate to low causality scores, and provide a framework to evaluate the causality of orthobunyaviruses that may newly emerge in the future.

Granger Causality Analysis of Foreign Trade Impact on Economic Growth: Case of Azerbaijan

Main purpose of the investigation is to define existing of causality relationship between foreign trade activity of Azerbaijan and economic growth. There were used OLS method and cointegration between some macroeconomic indicators. Main conclusion is that there is not causality effect between import and GDP, but GDP growth is cause for changing import for lag=3. As well as there is causality effect between GDP growth and export. But there is not strong causality effect between foreign trade openness, foreign trade freedom and economic growth.

The Effect of Copper Price Shock on the Relationship between Government Revenue and Expenditure: Testing the Fiscal Stability Law of Mongolia

This study empirically investigates the relationship between government revenue, government expenditure and the copper price in Mongolia, a resource abundant country. Using quarterly data of government revenue, expenditure and international copper price from 2000 to 2015, the results of auto regression (VAR) show that there is a strong causality from revenue to expenditure, while increase in expenditure, most likely, is not accompanied by rises in revenue. This result is consistent with the revenue-spent hypothesis. Moreover, the result also indicates that copper price shock increases revenue, but decreases expenditure. This finding supports the assumption that the Mongolian government follows its Fiscal Stability Law, a strategy that intends to maintain the stability and sustainability of the government budget.

Granger causality of the local Hadley cell and large-scale cloud cover over South Africa

This study demonstrates that Hadley cell dynamics could be used as a proxy to determine cloud cover and thus solar energy potential over South Africa. Granger causality was used to investigate causal interactions between the Hadley cell and cloud cover for the period 1980–2015, and such links were established. Areas of strong causality are found over the northwestern parts of South Africa. Moreover, weak causality from cloud cover to the Hadley cell does exist, with vertical velocity being the main variable responsible for this causality, which hence indirectly links cloud cover to Hadley cell causality.

The rise of national central banks' TARGET balances: a response to Andrea Terzi

In response to our paper, ‘ECB monetary expansions and euro area TARGET2 imbalances: a balance-of-payment-based decomposition,’ Professor Andrea Terzi has criticized our approach of TARGET2 balance decomposition, by highlighting a lack of causality between balance-of-payments (BP) flows and TARGET2 net balances. Proving a strong causality link was not within the scope of our paper; while acknowledging that causal relationships are difficult to prove from data that have to fulfill an accounting identity, we still believe that useful information can be extracted from the analysis of BP accounting correspondences. From this perspective a long-term BP reconstruction for Italy and Germany is performed that confirms Terzi's claim about the rise of TARGET2 balances under specific monetary policy configurations.

International tourism demand, number of airline seats and trade triangle: Evidence from New Zealand partners

This article examines the three-way relationship between international tourism demand, airline economy seats and international trade for New Zealand together with its key trading/tourism partners. We have found that airline economy seats are the important factor for determining tourism demand among New Zealand's tourism partners except for richer economies, like the United States and Japan. Trade volume does not have strong causality relationship to tourism demand in particular for trading partners, like Japan, Korea, Singapore and the United States. However, especially after the global financial crisis, it is observed that trade volumes help to boost the number of airline economy seats available (airline seat capacity) between New Zealand and its trading partners.

The perfect regression and causality test: A solution to regression problems

Summary We introduce a method that eliminates the specification error and spurious relationships in regression. In addition, we introduce a test of strong causality. Furthermore, hypothesis testing (inference) becomes almost unneeded. Moreover, this method virtually resolves error problems such as heteroscedasticity, autocorrelation, non-stationarity and endogeneity.

Hierarchizing graph-based image segmentation algorithms relying on region dissimilarity

This article is a first attempt towards a general theory for hierarchizing non-hierarchical image segmentation method depending on a region-dissimilarity parameter which controls the desired level of simpli fication: each level of the hierarchy is “as close as possible” to the result that one would obtain with the non-hierarchical method using the corresponding scale as simplification parameter. The introduction of this hierarchization problem in the form of an optimization problem, as well as the proposed tools to tackle it, is an important contribution of the present article. Indeed, with the hierarchized version of a segmentation method, the user can just select the level in the hierarchy, controlling the desired number of regions or can leverage on any of the tools introduced in hierarchical analysis. The main example investigated in this study is the criterion proposed by Felzenszwalb and Huttenlocher for which we show that the results of the hierarchized version of the segmentation method are better than those of the original one with the added property that it satisfies the strong causality and location principles from scale-sets image analysis. An interesting perspective of thiswork, considering the current trend in computer vision, is obviously, on a specific application, to use learning techniques and train a criterion to choose the correct region.

Insider Trading Activities and Returns of German Blue Chips

The aim of this paper is to investigate the causality between stock returns and insider open market transactions. The Dumitrescu-Hurlin (2012) heterogeneous approach to panel Granger causality is chosen to examine the relationship. The investigation is conducted on the 30 most traded German blue chips during the period of 2006–2014. The strong causality is revealed in the one-month period. Thus, stock returns may be used to predict future insider trading activity. The strong causality between stock returns and future insider buying and selling transactions is further confirmed with three out of four employed insider trading indices. The fact of the legal insider trade (either buy or sell) is more important than its volume. The reverse relationship is weak and valid only for longer time horizon of twelve months. Our results indicate that insider traders do not degrade the market efficiency in the long run.