Percolative conductivity in alkaline earth silicate melts and glasses

Ion conducting $(CaO)_x(SiO_2)_{1-x}$ glasses and melts show a threshold behaviour in dc conductivity near $x=x_t=0.50$, with conductivities increasing linearly at $x>x_t$. We show that the behaviour can be traced to a rigid ($x0.50$) elastic phase transition near $x=x_t$. In the floppy phase, conductivity enhancement is traced to increased mobility or diffusion of $Ca^{2+}$ carriers as the modified network elastically softens.Comment: 15 pages, 5 figures. Europhysics Letters (2003), in pres

Do returns and volatility spillovers exist across tech stocks, cryptocurrencies and NFTs?

This study examines the connectedness between technology stocks, cryptocurrencies, and non-fungible tokens (NFTs) using daily returns and risk data. We found that while there is strong connectedness within asset classes, connectedness between different types of assets is weak. Structural breaks in the VAR system did not change the degree of connectedness. Our findings suggest that interconnectivity between these assets is not significant enough to indicate a high level of correlation. This research provides valuable insights into the interplay between these markets and suggests diversifying portfolios to mitigate risks associated with these assets

Biosynthesis of spathulenol and camphor stand as a competitive route to artemisinin production as revealed by a new chemometric convergence approach based on nine locations’ field-grown Artemesia annua L.

Since isopentenyl diphosphate (IPP) and its isomer dimethylallyl diphosphate (DMAPP) are the universal precursors of both essential oil components, and the antimalarial agent artemisinin and its derivatives in Artemesia annua L., this paper aims to correlate the spotted differences in their concentrations by screening Artemesia annua L. field-grown in nine locations around the world that may reveal the role of any these compounds as precursors or competitors in the biosynthetic pathway of the sesquiterpene lactone : artemisinin. Principal component analysis (PCA) revealed that artemisinin is positively correlated to β-pinene, 1.8-cineole, sabinene hydrate, borneol and 1-octen-3-ol; but negatively to artemisinic acid and β-caryophyllene oxide. Hierarchical cluster analysis (HCA) classified locations into two distinct groups in which artemisinin concentration stood as the main driving factor to build similarities between the locations. In parallel, an improved convergence approach based on idiosyncratic similarities able to capture heterogeneity across individuals is proposed, which was able to classify compounds into four distinct clusters. Artemisinin appeared to be cross-linked to p-cymene, cis-carvyle acetate, 4-terpinene-1-ol, β-caryophyllene, β-farnesene, β-selinene, α-selinene, β-caryophyllene oxide and α-costol. It is interesting to see how camphor and spathulenol behaved as a distinct cluster group, which suggests that biosynthesis of these two compounds follows a different but a competitive pathway ; thus limiting their production could be a key to control and enhance the production of artemisinin

Delocalization of edge states in topological phases

The presence of a topologically non-trivial discrete invariants implies the existence of gapless modes in finite samples, but it does not necessarily imply their localization. The disappearance of the indirect energy gap in the bulk generically leads to the absence of localized edge states. We illustrate this behavior in two fundamental lattice models on the single-particle level. By tuning a hopping parameter the indirect gap is closed while maintaining the topological properties. The inverse participation ratio is used to measure the degree of localization.Comment: 5 pages including 6 figures and 4 pages supplement including 8 figur

Correlation between floppy to rigid transitions and non-Arrhenius conductivity in glasses

Non-Arrhenius behaviour and fast increase of the ionic conductivity is observed for a number of potassium silicate glasses $(1-x)SiO_2-xK_2O$ with potassium oxide concentration larger than a certain value $x=x_c=0.14$. Recovering of Arrhenius behaviour is provided by the annealing that enhances densification. Conductivity furthermore obeys a percolation law with the same critical concentration $x_c$. These various results are the manifestation of the floppy or rigid nature of the network and can be analyzed with constraint theory. They underscore the key role played by network rigidity for the understanding of conduction and saturation effects in glassy electrolytes.Comment: 4 pages, 4 EPS figure

Statistical calibration of CFD modelling for street canyon flows

CFD simulations of complex outdoor environments present a significant modelling challenge. Simulations of airflow within an idealized street canyon are performed here. We test the model sensitivity to the empirical constants contained within the κ-ε turbulence model and examine how a systematic variation of these values could produce improved prediction of the turbulent kinetic energy when compared against wind tunnel data. The Bayesian statistical calibration shows the range of values the constants should take. This results in improved CFD simulations in the region of flow inside the street canyon, which is normally very difficult to resolve accurately in CFD models