The Impact of the Measure Used to Calculate the Distance between Exchange Rate Time Series on the Topological Structure of the Currency Network.

Structural properties of the currency market were examined with the use of topological networks. Relationships between currencies were analyzed by constructing minimal spanning trees (MSTs). The dissimilarities between time series of currency returns were measured in various ways: by applying Euclidean distance, Pearson's linear correlation coefficient, Spearman's rank correlation coefficient, Kendall's coefficient, partial correlation, dynamic time warping measure, and Kullback-Leibler relative entropy. For the constructed MSTs, their topological characteristics were analyzed and conclusions were drawn regarding the influence of the dissimilarity measure used. It turned out that the strength of most types of correlations was highly dependent on the choice of the numeraire currency, while partial correlations were invariant in this respect. It can be stated that a network built on the basis of partial correlations provides a more adequate illustration of pairwise relationships in the foreign exchange market. The data for quotations of 37 of the most important world currencies and four precious metals in the period from 1 January 2019 to 31 December 2022 were used. The outbreak of the COVID-19 pandemic in 2020 and Russia's invasion of Ukraine in 2022 triggered changes in the topology of the currency network. As a result of these crises, the average distances between tree nodes decreased and the centralization of graphs increased. Our results confirm that currencies are often pegged to other currencies due to countries' geographic locations and economic ties. The detected structures can be useful in descriptions of the currency market, can help in constructing a stable portfolio of the foreign exchange rates, and can be a valuable tool in searching for economic factors influencing specific groups of countries.

Resistance of postprandial gastric functions and autonomic balance to taste stimulation.

Exposure to unpleasant tastes leads to disturbances of interdigestive gastric myoelectrical activity (GMA) and may affect sympathetic/parasympathetic balance (SPB). We made a careful study to determine whether taste stimulation modulates the postprandial GMA, SPB, and gastric emptying (GE) of a solid meal. Eighteen healthy volunteers (9F/9M) entered the study. On six separate days, we recorded a four-channel electrogastrogram from each volunteer during a 35-min fasting period, then for 90 min after ingestion of a solid test meal of 300 kcal. GE was measured using a 13C-octanoic acid breath test. Heart rate variability (HRV) analysis was simultaneously performed. At the start of the 21st min after the test meal, subjects received an agar cube delivering either a sweet, salty, sour, or bitter taste, which they kept in the mouth for 35 min. Control procedures involved sessions performed with a tasteless agar cube, and without any stimulation. There was no effect of the experimental intervention upon the relative power share of particular GMA rhythms. Stimulation with the salty and the bitter taste evoked a statistically significant increase in the dominant frequency, whereas the sweet and sour taste did not affect it. Taste stimulation did not interfere with the meal-induced rise in the dominant power, nor affect slow wave coupling. The kinetics of the solid GE remained unchanged by the intervention. None of the taste stimulations affected the postprandial SPB. Taste stimulation elicited after ingestion of a meal, in contrast to that during a fast, did not adversely modify the postprandial pattern of either the GMA or SPB, nor affect the GE of solids.