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Interfacial atomic vibration:A key dynamic characteristic for heterogeneous nucleation substrates
No full textHeterogeneous nucleation during metal solidification is a key pathway for achieving grain refinement. However, due to the challenges in experimentally probing the solid-liquid interface, the underlying atomistic mechanisms remain unclear. Although classical lattice matching theories provide a framework for geometric compatibility, the static rigid models inherently neglect the strong atomic dynamics characteristic of high-temperature interfaces. In this study, ab initio molecular dynamics (AIMD) with on-the-fly machine learning force field (MLFF) is applied to evaluate the templating efficiency of different potential substrates for Al alloys. The templating efficiency is defined here as the capability to induce structural ordering within the pre-nucleation layer (PNL). The results show that a deep interfacial potential well (Ew) provides the necessary driving force to localize liquid atoms, whereas excessive atomic vibrations spatially disrupt this ordering process. The effect of temperature prompts the integration of interface dynamics into geometric mismatch. The dynamic stability is the main prerequisite for the initial PNL formation near the liquidus, and the epitaxial growth of PNL into stable nuclei is constrained by the accumulated lattice strain as the temperature decreases. Based on this dynamic-static mechanism and engineering considerations, a (Ta, Ti)B2/Al3Ta substrate is designed, which achieves significant grain refinement in Al-Si alloys. These findings deepen the understanding of heterogeneous nucleation and highlight interfacial dynamics as an important factor for the design of nucleation substrates.</p
Random Permutation Circuits Beyond Qubits are Quantum Chaotic
No full textRandom permutation circuits were recently introduced as minimal models for local many-body dynamics that can be interpreted both as classical and quantum. Standard dynamical complexity indicators such as damage spreading and out-of-time-order correlators (OTOCs), show that these systems exhibit sensitivity to initial conditions in the classical setting and operator scrambling in the quantum setting. Here, we address their quantum chaoticity - a stricter property - by studying the time evolution of local operator entanglement (LOE). We show that the behaviour of LOE in random permutation circuits depends on the dimension of the local configuration space q. When q = 2, i.e. the circuits act on qubits, random permutations are Clifford and the LOE of any local operator is bounded by a constant, indicating that they are not truly chaotic. On the other hand, when the dimension of the local configuration space exceeds two, the LOE grows linearly in time. We prove this in the limit of large q and present numerical evidence that a three-dimensional local configuration space is sufficient for a linear growth of LOE. Our findings highlight that quantum chaos can be produced by essentially classical dynamics. Moreover, we show that LOE can be defined also in the classical realm and put it forward as a universal indicator chaos, both quantum and classical
Domestic Dispute, Foreign Forum:the Nigerian Court of Appeal’s Approach to a South African Choice of Court Agreement
No full textThis article examines the Nigerian Court of Appeal’s decision in Sqimnga (Nig.) Ltd v Systems Applications Products (Nig.) Ltd, which upheld an exclusive South African choice of court clause in a dispute between two Nigerian companies. This very recent decision affirms the Nigerian judiciary’s commitment to party autonomy, emphasising the principles of pacta sunt servanda and consensu facit legem, and applying the ‘strong cause’ test derived from The Eleftheria. The Court held that a party seeking to litigate in Nigeria contrary to a foreign jurisdiction agreement bears a strict evidential burden, which must be discharged through affidavit evidence rather than pleadings or counsel submissions. In this respect, the decision is consistent with established Nigerian authority, notably Nika Fishing Company Ltd v Lavina Corporation.Beyond its doctrinal correctness, the article highlights important unresolved issues in Nigerian conflict of laws. It questions whether a dispute that is domestic in substance – between Nigerian parties, concerning a contract concluded and performed in Nigeria – should be internationalised solely by a foreign choice of court clause. Drawing on comparative perspectives from South African law, English common law, the Hague Choice of Court Convention, and the Brussels I Recast, the article demonstrates that different legal systems adopt divergent approaches to this question. It concludes that Sqimnga exposes a need for deeper comparative engagement in shaping the future development of Nigerian private international law
Tides of tension:Exploring the blue economy through stakeholder narrations
No full textThe Blue Economy concept combines the views of oceans and seas as areas of economic growth, industrialization, and development, on the one hand, and as vulnerable marine ecosystems that need to be protected, on the other hand. Drawing on a concept driven by managerial practice in ocean-related industries, national and transnational institutions, and policymakers, this study applies abductive reasoning to explore the tension between these priorities and contribute to a holistic understanding of the Blue Economy. First, we establish the Blue Economy as a transitory research context in studies across multiple disciplines. Second, we describe it using three lenses from interdisciplinary literature: place, development, and sustainability. Third, we ground the Blue Economy in reality, using narrations around these lenses that we extract from data collected during four online workshops with diverse stakeholders. The narrations show how stakeholders deal with the conundrum arising from issues around ownership and control (place), the economic needs of countries and communities (development), and the quest for resilient ecosystems (sustainability). Finally, applying grid-group analysis to evaluate the narrations lays bare stakeholders’ antagonistic perspectives. We discuss techno-solutionism, localism, and transnationalism as at least temporarily acceptable responses to competing priorities that embrace the interplay between place, development, and sustainability and may inspire recommendations for policymakers
The evolution of nulling in pulsars
No full textNulling is a phenomenon where the emission from a pulsar becomes undetectable (or significantly weaker) for a relatively short period of time, followed by a return to a normal emission state. The time-scale of nulling ranges from a few pulse periods to many hours or even days. The fraction of time a nulling pulsar spends in a null state varies across the population of canonical pulsars, from 0 to 95 per cent. The long-term behaviour of a pulsar’s nulling fraction, however, is currently unknown, as published values have typically been obtained through single observations. Here, we present the first long-term analysis of nulling behaviour in eight pulsars observed in the Parkes Multibeam Pulsar Survey over the course of eight to ten years. We also apply a new Bayesian method for pulse-energy analysis, yielding posterior estimates of the nulling fraction per observation. In several cases, the nulling affects only specific components of the pulse profile, rather than the entirety of the emission. Our analysis reveals that, while most pulsars show no significant trend in their nulling fraction over time, a subset exhibit some evidence for non-zero gradients in nulling fraction. In particular, PSRs J1048–3832, J1745–3040, and J1825–0935 show statistically significant trends over the span of the data. Studying the behaviour of nulling over years and decades is valuable as it can provide insights into the physical emission processes within pulsars. Studying how nulling evolves also provides valuable insights into pulsar evolution and the characterization of the broader pulsar population
Entanglement dynamics and Page curves in random permutation circuits
No full textThe characterization of ensembles of many-qubit random states and their realization via quantum circuits are crucial tasks in quantum-information theory. In this work, we study the ensembles generated by quantum circuits that randomly permute the computational basis, thus acting classically on the corresponding states. We focus on the averaged entanglement and present two main results. First, we derive generically tight upper bounds on the entanglement that can be generated by applying permutation circuits to arbitrary initial states. We show that the late-time “entanglement Page curves” are bounded in terms of the initial state participation entropies and their overlap with the “maximally antilocalized” state. Generally speaking, this result states that the quantum correlations generated by classical circuits are bounded in terms of some quantum property of the initial state (namely, the degree to which it can be written as a superposition of classical states). Second, comparing the averaged Rényi-2 entropies generated by (1) an infinitely deep random circuit of two-qubit gates and (2) global random permutations, we show that the two quantities are different for finite N but the corresponding Page curves coincide in the thermodynamic limit. We also discuss how these conclusions are modified by additional random phases or considering circuits of k-local gates with k ≥ 3. Our results are exact and highlight the implications of classical features on entanglement generation in many-body systems.</p
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