Why are very short times so long and very long times so short in elastic waves?

In a first study of thermoelastic waves, such as on the textbook of Landau and Lifshitz, one might at first glance understand that when the given period is very short, waves are isentropic because heat conduction does not set in, while if the given period is very long waves are isothermal because there is enough time for thermalization to be thoroughly accomplished. When one pursues the study of these waves further, by the mathematical inspection of the complete thermoelastic wave equation he finds that if the period is very short, much shorter than a characteristic time of the material, the wave is isothermal, while if it is very long, much longer than the characteristic time, the wave is isentropic. One also learns that this fact is supported by experiments: at low frequencies the elastic waves are isentropic, while they are isothermal when the frequencies are so high that can be attained in few cases. The authors show that there is no contradiction between the first glance understanding and the mathematical treatment of the elastic wave equation: for thermal effects very long periods are so short and very short periods are so long.Comment: 7 pages, submitted to European Journal of Physic

A factor augmented vector autoregressive model and a stacked de-noising auto-encoders forecast combination to predict the price of oil

The following dissertation aims to show the benefits of a forecast combination between an econometric and a deep learning approach. On one side, a Factor Augmented Vector Autoregressive Model (FAVAR) with naming variables identification following Stock and Watson (2016)1; on the other side, a Stacked De-noising Auto-Encoder with Bagging (SDAE-B) following Zhao, Li and Yu (2017)2 are implemented. From January 2010 to September 2018 Two-hundred-eighty-one monthly series are used to predict the price of the West Texas Intermediate (WTI). The model performance is analysed by Root Mean Squared Error (RMSE), Mean Absolute Percentage Error (MAPE) and Directional Accuracy (DA). The combination benefits from both SDAE-B’s high accuracy and FAVAR’s interpretation features through impulse response functions (IRFs) and forecast error variance decomposition (FEVD)

Pragmatism and Emergentism : In Chauncey Wright’s Evolutionary Philosophy

The notion of \u201cemergence\u201d has recently received renewed attention in research fields ranging from biology to cognitive sciences and philosophy of mind. Today\u2019s concept of \u201cemergence\u201d incorporates a long history of philosophical debates and reflections that can be traced back to James and John Stuart Mill and nineteenth-century associationist philosophy. This tradition reached its theoretical maturity in the early twentieth century with so-called classical British emergentism, which gained the attention of pragmatist philosophers from the beginning. In the current literature exploring the relationship between Pragmatism and the emergentist tradition, almost nothing is said about the interesting case of Chauncey Wright (1830-1875), a follower of J. S. Mill and A. Bain, and a crucial figure for the origins of pragmatist philosophy. After a brief historical introduction about the history of the notion of \u201cemergence\u201d and its relationship to classical Pragmatism, the paper aims to examine Wright\u2019s philosophy in relation, on one hand, to the pragmatist tradition and, on the other hand, to the problem of emergence. In the wake of Wright\u2019s original interpretation of Darwin\u2019s evolutionary theory, the article focuses on the key notions of \u201cnovelty\u201d and \u201cnew uses,\u201d through which Wright developed an \u201cemergentist\u201d philosophy that was well ahead of its time and attracted the interest of Samuel Alexander, one of the major philosophers of classical British emergentism. In the second part, the paper analyzes Wright\u2019s reflections about the origin of human self-consciousness as a paradigmatic case of authentic evolutionary novelty. In the final part, the article focuses on the kind of pragmatic realism sketched out by Wright and summarizes the most important aspects to have emerged during the scholarly debate on the topic

Programming scale-free optics in disordered ferroelectrics

Using the history-dependence of a dipolar glass hosted in a compositionally-disordered lithium-enriched potassium-tantalate-niobate (KTN:Li) crystal, we demonstrate scale-free optical propagation at tunable temperatures. The operating equilibration temperature is determined by previous crystal spiralling in the temperature/cooling-rate phase-space

Evidence of double-loop hysteresis in disordered ferroelectric crystal

Double-loop electric-field vs polarization hysteresis is investigated in a depoled compositionally disordered lithium-enriched potassium tantalate niobate crystal. Comparing electro-optic response and dielectric spectroscopy indicates that the anomalous response occurs for those temperatures in which the sample also manifests a temperature hysteresis in the low-frequency dielectric function. An electric-field hysteresis at concurrent temperatures suggests an underlying role of reorienting mesoscopic polar regions that accompany the nonergodic phase. Published under license by AIP Publishing

Mosaic evolution in hominin phylogeny : meanings, implications, and explanations

In paleoanthropological literature, the use of the term "mosaic" (mosaic evolution, mosaic trait, mosaic species, and so on) is becoming more and more frequent. In order to promote a clarification of the use of the concept in literature, we propose here a classification in three different meanings of the notion of mosaic in human evolution: 1) morphological (inter-specific and intra-specific) instability in a certain phase of a branched phylogeny; 2) multiple trajectories and versions of the same adaptive trait in a branched phylogeny; 3) the trait itself as a complex mosaic of sub-traits with different phylogenetic stories (as is the case in language). We argue that the relevance of such mosaic patterns needs a macro-evolutionary interpretation, which takes into consideration the interaction between general selective pressures (promoting different versions of the same adaptation) and a cladogenetic approach in which speciation played a crucial role, due to ecological instability, habitat fragmentation, and geographical dispersals in human evolution

Photorefractive light needles in glassy nanodisordered KNTN

We study the formation of 2D self-trapped beams in nanodisordered potassium-sodium-tantalate-niobate (KNTN) cooled below the dynamic glass transition. Supercooling is shown to accelerate the photorefractive response and enhance steady-state anisotropy. Effects in the excited state are attributed to the anomalous slim-loop polarization curve typical of relaxors dominated by non-interacting polar-nano-regions