Understanding, predicting, and tuning the fragility of vitrimeric polymers

Fragility is an empirical property that describes how abruptly a glass-forming material solidifies upon supercooling. The degree of fragility carries important implications for the functionality and processability of a material, as well as for our fundamental understanding of the glass transition. However, the microstructural properties underlying fragility still remain poorly understood. Here, we explain the microstructure–fragility link in vitrimeric networks, a novel type of high-performance polymers with unique bond-swapping functionality and unusual glass-forming behavior. Our results are gained from coarse-grained computer simulations and first-principles mode-coupling theory (MCT) of star-polymer vitrimers. We first demonstrate that the vitrimer fragility can be tuned over an unprecedentedly broad range, from fragile to strong and even superstrong behavior, by decreasing the bulk density. Remarkably, this entire phenomenology can be reproduced by microscopic MCT, thus challenging the conventional belief that existing first-principles theories cannot account for nonfragile behaviors. Our MCT analysis allows us to rationally identify the microstructural origin of the fragile-to-superstrong crossover, which is rooted in the sensitivity of the static structure factor to temperature variations. On the molecular scale, this behavior stems from a change in dominant length scales, switching from repulsive excluded-volume interactions to intrachain attractions as the vitrimer density decreases. Finally, we develop a simplified schematic MCT model which corroborates our microscopically founded conclusions and which unites our findings with earlier MCT studies. Our work sheds additional light on the elusive structure–fragility link in glass-forming matter and provides a first-principles–based platform for designing amorphous materials with an on-demand dynamic response.

The Long Memory of Order Flow in the Foreign Exchange Spot Market

We study the long memory of order flow for each of three liquid currency pairs on a large electronic trading platform in the foreign exchange (FX) spot market. Due to the extremely high levels of market activity on the platform, and in contrast to existing empirical studies of other markets, our data enables us to perform statistically stable estimation without needing to aggregate data from different trading days. We find strong evidence of long memory, with a Hurst exponent [Formula: see text], for each of the three currency pairs and on each trading day in our sample. We repeat our calculations using data that spans different trading days, and we find no significant differences in our results. We test and reject the hypothesis that the apparent long memory of order flow is an artifact caused by structural breaks, in favor of the alternative hypothesis of true long memory. We therefore conclude that the long memory of order flow in the FX spot market is a robust empirical property that persists across daily boundaries.

Only narratives can reflect the experience of objectivity: effective persuasion

Purpose – The purpose of this paper is to explore the differences between objective language and narratives and how differences affect rhetoric. Design/methodology/approach – Conceptual implications are drawn from an analysis and discussion of the literature in the fields of autopoiesis, meanings and narratives. Findings – Only narratives convey the experience of objectivity, which makes them more effective to persuade people to change than just providing “objective” data and explanatory knowledge. Originality/value – The paper discusses how the projection of meaning is not an experience but knowledge. Meaning is experienced as an empirical property of the perceived.

A NONLINEAR DYNAMICS PERSPECTIVE OF WOLFRAM'S NEW KIND OF SCIENCE PART IX: QUASI-ERGODICITY

Our scientific odyssey through the theory of 1-D cellular automata is enriched by the definition of quasi-ergodicity, a new empirical property discovered by analyzing the time-1 return maps of local rules. Quasi-ergodicity plays a key role in the classification of rules into six groups: in fact, it is an exclusive characteristic of complex and hyper Bernoulli-shift rules. Besides introducing quasi-ergodicity, this paper answers several questions posed in the previous chapters of our quest. To start with, we offer a rigorous explanation of the fractal behavior of the time-1 characteristic functions, finding the equations that describe this phenomenon. Then, we propose a classification of rules according to the presence of Isles of Eden, and prove that only 28 local rules out of 256 do not have any of them; this result sheds light on the importance of Isles of Eden. A section of this paper is devoted to the characterization of Bernoulli basin-tree diagrams through modular arithmetic; the formulas obtained allow us to shorten drastically the number of cases to take into consideration during numerical simulations. Last but not least, we present some theorems about additive rules, including an analytical explanation of their scale-free property.

Mechanisms Underlying Hardness Numbers

ABSTRACTRelationships of indentation hardness numbers to to other physical properties are demonstrated. They differ depending on the type of chemical bonding; metals, alloys ionic, covalent, and metal-metalloid. The properties are: shear modulus; ionic charge; band-gap density; polarizability; and formation energy, respectively. In each case the rationale is provided. The concept of a “bonding Modulus” is introduced. It is concluded that the conventional wisdom that hardness is a purely empirical property does not hold. Phase transformations and indentation hardness are connected broadly.

Mechanisms Underlying Hardness Numbers

ABSTRACTRelationships of indentation hardness numbers to to other physical properties are demonstrated. They differ depending on the type of chemical bonding; metals, alloys ionic, covalent, and metal-metalloid. The properties are: shear modulus; ionic charge; band-gap density; polarizability; and formation energy, respectively. In each case the rationale is provided. The concept of a “bonding Modulus” is introduced. It is concluded that the conventional wisdom that hardness is a purely empirical property does not hold. Phase transformations and indentation hardness are connected broadly.

Humean Causation and Kim's Theory of Events

In recent years Jaegwon Kim has propounded and elaborated an influential theory of events. He takes an event to be the exemplification of an empirical property (or n-adic attribute) by a concrete object (or several concrete objects) at a time. He also has proposed and endorsed a version of the “Humean” tradition concerning causation: the view that causal relations between concrete events depend upon general "covering laws." But although his explication of the covering-law conception of causation seems quite natural within the framework of his theory, it gives rise to a serious problem: in numerous garden-variety instances of causation, the Humean conditions (as Kim specifies them) are not satisfied. In this paper I shall suggest a way to modify Kim's theory of events in order to reconcile it with his treatment of causality.