Pronounced asymmetry in the crystallization behavior during constant heating and cooling of a bulk metallic glass-forming liquid

The crystallization behavior of the supercooled bulk metallic glass-forming Zr41Ti14Cu12Ni10Be23 liquid was studied with different heating and cooling rates. A rate of about 1 K/s is sufficient to suppress crystallization of the melt upon cooling from the equilibrium liquid. Upon heating, in contrast, a rate of about 200 K/s is necessary to avoid crystallization. The difference between the critical heating and cooling rate is discussed with respect to diffusion-limited growth taking classical nucleation into account. The calculated asymmetry of the critical heating and cooling rate can be explained by the fact that nuclei formed during cooling and heating are exposed to different growth rates

Viscous flow and crystallization of bulk metallic glass forming liquids

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. An experimental setup was designed and implemented to measure the flow behavior of liquids in the viscosity range from [...] Pa s to [...] Pa s. The viscosity of the [...] (V1) bulk metallic glass forming alloy was measured over a temperature range from 927 K to 1173 K. At the liquidus temperature, the viscosity is 2.3 Pa s, which is about three orders of magnitude larger than the viscosity of a pure metallic liquid. The free volume theory as formulated by Cohen and Grest describes the temperature dependence of the viscosity of V1 over 14 orders in magnitude. The high viscosity of V1 above the liquidus temperature stabilizes the liquid against convective flow due to temperature gradients and allows for diffusion experiments in the equilibrium liquid. The temperature dependence of the diffusivity of large atoms like A1 or Au scales with the viscosity. The time scales obtained from the viscosity measurements suggest that above the calorimetric glass transition region the diffusion of small and medium sized atoms is governed by thermally activated jumps. Liquid V1 could be successfully supercooled inside high purity graphite crucibles without changing the stability of the supercooled liquid with respect to crystallization compared to levitated samples. The sluggish kinetics that are reflected in the high viscosity in the supercooled liquid state contribute significantly to the good glass forming ability of the alloy. The critical cooling rate is about 1 K/s. The onset of crystallization under isothermal conditions as well as upon heating from the amorphous state was studied in detail. The critical heating rate to bypass crystallization was measured to be 200 K/s and the difference between the critical cooling and critical heating rate can be qualitatively understood in the framework of nucleation and growth. However, the observed deviations from classical steady state nucleation behavior indicate a more complex crystallization mechanism. Rheological and crystallization studies at constant shear rate suggest that changes in the morphology of the supercooled liquid of V1 occur as a precursor of crystallization

Bayesian estimation of generalized partition of unity copulas

This paper proposes a Bayesian estimation algorithm to estimate Generalized Partition of Unity Copulas (GPUC), a class of nonparametric copulas recently introduced by [18]. The first approach is a random walk Metropolis-Hastings (RW-MH) algorithm, the second one is a random blocking random walk Metropolis-Hastings algorithm (RBRW-MH). Both approaches are Markov chain Monte Carlo methods and can cope with ˛at priors. We carry out simulation studies to determine and compare the efficiency of the algorithms. We present an empirical illustration where GPUCs are used to nonparametrically describe the dependence of exchange rate changes of the crypto-currencies Bitcoin and Ethereum

The Wagner Group—A Preliminary Update

This edition focuses on the Wagner Group private military company, providing an update to our issue 290 on the same topic. This issue focuses on developments after the Wagner mutiny. First, Stephen Aris summarizes the context of the mutiny and its aftermath, then Andreas Heinemann-Grüder goes on to examine Wagner’s role in Russia’s political regime and the state’s attempts to regain control. Moreover, Niklas Masuhr examines Russia’s post-Prigozhin Footprint in Africa and Kimberly Marten looks at Russian Foreign Paramilitary Outfits beyond Wagner.Diese Ausgabe befasst sich mit der privaten Militärfirma Wagner Group und befasst sich in Aktualisierung unserer Ausgabe 290 zum selben Thema mit den Entwicklungen nach der Wagner-Meuterei. Zunächst fasst Stephen Aris den Kontext der Meuterei und ihrer Folgen zusammen, dann untersucht Andreas Heinemann-Grüder die Rolle Wagners im politischen System Russlands und die Versuche des Staates, die Kontrolle wiederzuerlangen. Darüber hinaus beschreibt Niklas Masuhr Russlands Engagement in Afrika nach dem Tod Prigoshins und Kimberly Marten befasst sich mit weiteren russischen Militärfirmen, die als Alternative zur Wagner Gruppe dienen können.ISSN:1863-042