Elementary Processes Research Articles

First-principles study on silicon emission from interface into oxide during silicon thermal oxidation

Using the first-principles calculation, the diffusion path is explored in the Si emission from the interface into the Si oxide surface during the Si oxidation process, by assuming that the Si emission dominantly consists of a SiO interstitial diffusion. Searching for the diffusion path was succeeded and the energy profile of diffusion path can be evaluated. At this time, only three elementary processes, such as O vacancy transfer, coordination number conversion of Si, and ACBD bond order conversion, were just considered. It has been confirmed that the SiO interstitial moves in the oxide with sequentially kicking the neighboring Si and O like a billiards, and that the kicked-out Si and O become a new SiO interstitial, while Si and O belonging to the old SiO interstitial are absorbed as a part of the oxide. Furthermore, the energy profile of similar diffusion path in bulk SiO2 crystal is also compared. It is revealed that the Si oxide layer is relatively flexible against structural deformation, and that the oxide surface is much more flexible, but that the oxide layer near the interface is less flexible due to the influence of the rather rigid Si substrate. The results indicate that our assumption on the Si emission in the Si oxidation process is fair, and that the SiO interstitial diffusion in the oxide film is inevitable in order to reduce the impact of volume expansion that occurs at the interface.

Stress-rupture behavior of a Re-containing Ni-base single crystal superalloy at high temperatures

A Re-containing Ni-base single crystal superalloy was used to investigate the elementary processes associated with stress-rupture behavior at different temperatures where the γʹ rafting occurs. At 900 °C, the rupture behavior is mainly determined by the multiplication of dislocations within the widening γ channels, which is closely linked with the propagation of microcracks along the inherent γ/γʹ interfaces. The rapid formation of lamella γ/γʹ raft structure, along with the developed-well interfacial dislocation networks, and its elastic instability are primarily responsible for the rupture behavior at 1100 °C. There is a clear curvature tendency in the Larson-Miller plot of stress-rupture lifetime in relation to stress at high temperatures. It indicates that the influence extent of γʹ rafting on stress-rupture behavior is sensitive to the acting conditions of temperature and stress.

The selective role of the orbital angular momentum on the reaction stereo-dynamics

This paper reports on the characterization of the stereo-dynamic controlling three different chemi-ionization reactions, recent objective of our study, since they participate to the balance of phenomena occurring in plasma, interstellar medium, planetary atmospheres, flames and lasers. The optical potential, obtained by a phenomenological method and defined in the whole space of the relative configurations of reagents, has been formulated in an accurate and internally consistent way for three different systems. Some cuts of the multidimensional potential, that asymptotically correlate with a specific fine level of the open shell atom and/or with a defined orientation of the molecular reagent, have been exploited in the present study to emphasize crucial features of the collision dynamics along selected entrance channels of the reactions. Consistently, basic quantities determining the topology of the reaction stereo-dynamics have been properly defined, emphasizing in the three cases relevant changes in the microscopic reaction evolution. Much attention focused on the selectivity of the orbital angular momentum, affecting each collision event at any chosen collision energy. It controls the relative weight of two different reaction mechanisms. The direct reaction mechanism is driven by short-range chemical forces, promoting, by direct electron transfer between reagents, a prototypical elementary oxidation reaction. The indirect mechanism, controlled by the combination of long-range chemical and physical forces, can be triggered by a virtual photon exchanged between reagents, promoting a sort of photo-ionization process. Obtained results and emphasized differences appear to be of general interest for many other elementary processes, more difficult to characterize at this level of detail.Graphic abstract

Electron transfer rules of minerals under pressure informed by machine learning

Electron transfer is the most elementary process in nature, but the existing electron transfer rules are seldom applied to high-pressure situations, such as in the deep Earth. Here we show a deep learning model to obtain the electronegativity of 96 elements under arbitrary pressure, and a regressed unified formula to quantify its relationship with pressure and electronic configuration. The relative work function of minerals is further predicted by electronegativity, presenting a decreasing trend with pressure because of pressure-induced electron delocalization. Using the work function as the case study of electronegativity, it reveals that the driving force behind directional electron transfer results from the enlarged work function difference between compounds with pressure. This well explains the deep high-conductivity anomalies, and helps discover the redox reactivity between widespread Fe(II)-bearing minerals and water during ongoing subduction. Our results give an insight into the fundamental physicochemical properties of elements and their compounds under pressure.

Phase synchronization of epicyclic motion due to gravitational scattering by wakes

ABSTRACT The swing amplification is one of the mechanisms for spiral arm formation and gravitational scattering of stellar orbits by a high-density region in a disc galaxy is considered as its elementary process. During the swing amplification, the epicycle phases of stars are synchronized. We previously showed that gravitational scattering by a softened point mass can synchronize the epicycle phases. Here, we expand upon our previous work to consider gravitational scattering by a finite-sized wake, which we model by using a prolate body. We numerically simulate the stellar motion under the influence of the wake gravity, and we investigate the dependence of the orbital evolution on the wake properties. We find that phase synchronization is more effective for a wake with a pitch angle around π/2, and that the phase synchronization depends on the wake shape. Even for realistic pitch angles i ≲ π/4 the phase synchronization can be more effective than that by the softened point mass. Increasing the impact parameter of stars and decreasing the wake pitch angle are shown to increase the axis ratio at which synchronization occurs. Linear trailing high-density patterns form around the wake and enlarge the wake itself.

Modeling of the P2M Past Fuel Melting Experiments with the FEMAXI-8 Code

In the Power to Melt and Maneuverability (P2M) project, a simulation exercise on two past power ramp experiments, xM3 on a medium-burnup rod and HBC4 on a high-burnup rod, was performed with the fuel performance code FEMAXI-8 to investigate fuel behavior under high-power and high-temperature conditions toward centerline fuel melting. In order to treat fuel melting, empirical melting temperature models have been incorporated into the FEMAXI-8 code. The present analysis gives reasonable predictions not only on cladding deformation but also on the fuel melting behavior of the HBC4 rod in which the UO2 liquidus temperature was reached during the transient. On the other hand, model improvement appears to be needed for a more accurate treatment of the fuel melting behavior of the xM3 rod in which the fuel center temperature reached the solidus line, whereas it may have not reached the liquidus line. A reasonable agreement of estimated fission gas release (FGR) with the measurement suggested that the high-temperature FGR at the given conditions is essentially a temperature-dependent phenomenon rate limited primarily by thermally activated elementary processes, such as fission gas diffusion.

3D phase-field simulations to machine-learn 3D information from 2D micrographs

A novel approach is developed to support retrieval of 3D information from 2D experimental micrographs. The approach utilizes 3D phase-field simulations to train an artificial intelligence machine. In a first step, the phase-field simulations have to be validated to reproduce microstructural features which characterize elementary processes which govern processing and high temperature service exposure. The qualified 3D simulation setup is then applied to produce a high number of 2D simulated micrographs by automated sectioning. These simulated micrographs are then used to train a gradient boosting regression model together with the 3D information from the simulations. In the final step, the model is applied to 2D experimental micrographs to retrieve the hidden 3D features. The approach is generally applicable to all kinds of metallic materials, minerals or ceramics which can be treated quantitatively by phase-field simulations. In this paper we concentrate on the process of directional coarsening, referred to as ‘rafting’, in the field of creep of single crystal Ni-base superalloys. The experimental and modeling aspects of the evolution of the volume fraction of the phase during long term creep are discussed.

The Fourfold Way to Gaussianity: Physical Interactions, Distributional Models and Monadic Transformations

The Central Limit Theorem stands as a milestone in probability theory and statistical physics, as the privileged, if not the unique, universal route to normal distributions. This article addresses and describes several other alternative routes to Gaussianity, stemming from physical interactions, related to particle-particle and radiative particle–photon elementary processes. The concept of conservative mixing transformations of random ensembles is addressed, as it represents the other main universal distributional route to Gaussianity in classical low-energy physics. Monadic ensemble transformations are introduced, accounting for radiative particle–photon interactions, and are intimately connected with the theory of random Iterated Function Systems. For Monadic transformations, possessing a thermodynamic constraint, Gaussianity represents the equilibrium condition in two limiting cases: in the low radiative-friction limit in any space dimension, and in the high radiative-friction limit, when the dimension of the physical space tends to infinity.

On the influence of crystallographic orientation on superelasticity - Fe-Mn-Al-Ni shape memory alloys studied by advanced in situ characterization techniques

The superelasticity of iron-based shape memory alloys is strongly influenced by microstructural features such as crystallographic orientation, size and morphology of grains, character of grain boundaries as well as volume fraction of precipitates. Furthermore, elementary processes such as formation of dislocations, interaction of dislocations with the austenite/martensite phase boundary, and the interaction of different martensite variants result in functional degradation. Advanced in situ characterization techniques like digital image correlation (DIC) and infrared thermography (IR-TG) corroborated by ex situ high resolution electron backscatter diffraction (HR-EBSD) and electron contrast channeling imaging (ECCI) were used to investigate the functional stability of the superelasticity of Fe–Mn–Al–Ni single crystals and oligocrystals under tensile and compressive loading. The early stabilization of martensite during repeated loading was attributed, besides other mechanisms, to the interaction of different martensite variants leading to the formation of dislocations, locally pinning the austenite/martensite interface.

Rovibrational internal energy transfer and dissociation of high-temperature oxygen mixture.

This work constructs a rovibrational state-to-state model for the O2 + O2 system leveraging high-fidelity potential energy surfaces and quasi-classical trajectory calculations. The model is used to investigate internal energy transfer and nonequilibrium reactive processes in a dissociating environment using a master equation approach, whereby the kinetics of each internal rovibrational state is explicitly computed. To cope with the exponentially large number of elementary processes that characterize reactive bimolecular collisions, the internal states of the collision partner are assumed to follow a Boltzmann distribution at a prescribed internal temperature. This procedure makes the problem tractable, reducing the computational cost to a comparable scale with the O2 + O system. The constructed rovibrational-specific kinetic database covers the temperature range of 7500-20 000K. The reaction rate coefficients included in the database are parameterized in the function of kinetic and internal temperatures. Analysis of the energy transfer and dissociation process in isochoric and isothermal conditions reveals that significant departure from the equilibrium Boltzmann distribution occurs during the energy transfer and dissociation phase. Comparing the population distribution of the O2 molecules against the O2 + O case demonstrates a more significant extent of nonequilibrium characterized by a more diffuse distribution whereby the vibrational strands are more clearly identifiable. This is partly due to less efficient mixing of the rovibrational states, which results in more diffuse rovibrational distributions in the quasi-steady-state distribution of O2 + O2. A master equation analysis for the combined O2 + O and O2 + O2 system reveals that the O2 + O2 system governs the early stage of energy transfer, whereas the O2 + O system takes control of the dissociation dynamics. The findings of the present work will provide a strong physical foundation that can be exploited to construct an improved reduced-order model for oxygen chemistry.

Seeing inferences: brain dynamics and oculomotor signatures of non-verbal deduction

We often express our thoughts through words, but thinking goes well beyond language. Here we focus on an elementary but basic thinking process, disjunction elimination, elicited by elementary visual scenes deprived of linguistic content, describing its neural and oculomotor correlates. We track two main components of a nonverbal deductive process: the construction of a logical representation (A or B), and its simplification by deduction (not A, therefore B). We identify the network active in the two phases and show that in the latter, but not in the former, it overlaps with areas known to respond to verbal logical reasoning. Oculomotor markers consistently differentiate logical processing induced by the construction of a representation, its simplification by deductive inference, and its maintenance when inferences cannot be drawn. Our results reveal how integrative logical processes incorporate novel experience in the flow of thoughts induced by visual scenes.

Cobalt-Catalyzed Diastereo- and Enantioselective Carbon-Carbon Bond Forming Reactions of Cyclobutenes.

Catalytic enantioselective functionalization of cyclobutenes constitutes a general and modular strategy for construction of enantioenriched complex cyclobutanes bearing multiple stereogenic centers, as chiral four-membered rings are common motifs in biologically active molecules and versatile intermediates in organic synthesis. However, enantioselective synthesis of cyclobutanes through such a strategy remained significantly limited. Herein, we report a series of unprecedented cobalt-catalyzed carbon-carbon bond forming reactions of cyclobutenes that are initiated through enantioselective carbometalation. The protocols feature diastereo- and enantioselective introduction of allyl, alkynyl, and functionalized alkyl groups. Mechanistic studies indicated an unusual 1,3-cobalt migration and subsequent β-carbon elimination cascade process occurred in the allyl addition. These new discoveries established a new elementary process for cobalt catalysis and an extension of diversity of nucleophiles for enantioselective transformations of cyclobutenes.

Rabi oscillations in a stretching molecule

Rabi oscillation is an elementary laser-driven physical process in atoms and artificial atoms from solid-state systems, while it is rarely demonstrated in molecules. Here, we investigate the bond-length-dependent Rabi oscillations with varying Rabi frequencies in strong-laser-field dissociation of H2+. The coupling of the bond stretching and Rabi oscillations makes the nuclei gain different kinetic energies while the electron is alternatively absorbing and emitting photons. The resulting proton kinetic energy spectra show rich structures beyond the prediction of the Floquet theorem and the well-accepted resonant one-photon dissociation pathway. Our study shows that the laser-driven Rabi oscillations accompanied by nuclear motions are essential to understanding the bond-breaking mechanism and provide a time-resolved perspective to manipulate rich dynamics of the strong-laser-field dissociation of molecules.

Discussion on Electron Temperature of Gas-Discharge Plasma with Non-Maxwellian Electron Energy Distribution Function Based on Entropy and Statistical Physics

Electron temperature is reconsidered for weakly-ionized oxygen and nitrogen plasmas with its discharge pressure of a few hundred Pa, with its electron density of the order of 1017m-3 and in a state of non-equilibrium, based on thermodynamics and statistical physics. The relationship between entropy and electron mean energy is focused on based on the electron energy distribution function (EEDF) calculated with the integro-differential Boltzmann equation for a given reduced electric field E/N. When the Boltzmann equation is solved, chemical kinetic equations are also simultaneously solved to determine essential excited species for the oxygen plasma, while vibrationally excited populations are solved for the nitrogen plasma, since the EEDF should be self-consistently found with the densities of collision counterparts of electrons. Next, the electron mean energy U and entropy S are calculated with the self-consistent EEDF obtained, where the entropy is calculated with the Gibbs's formula. Then, the "statistical" electron temperature Test is calculated as Test=[∂S/∂U]-1. The difference between Test and the electron kinetic temperature Tekin is discussed, which is defined as [2/(3k)] times of the mean electron energy U=⟨ϵ⟩, as well as the temperature given as a slope of the EEDF for each value of E/N from the viewpoint of statistical physics as well as of elementary processes in the oxygen or nitrogen plasma.

Vehicle Directional Cosine Calculation Method

Teaching kinematic rotations is a daunting task for even some of the most advanced mathematical minds. However, changing the paradigm can highly simplify envisioning and explaining the three-dimensional rotations. This paradigm change allows a high school student with an understanding of geometry to develop the matrix and explain the rotations at a collegiate level. The proposed method includes the assumption of a point (P) within the initial three-dimensional frame with axes (x^i, y^i, z^i). The method then utilizes a two-dimensional rotation view (2DRV) to measure how the coordinates of point P translate after a rotation around the initial axis. The equations are used in matrix notation to develop a rotation matrix for follow-on direction cosine matrixes. The method removes the requirement to use Euler’s formula, ultimately, providing a high school student with an elementary and repeatable process to compose and explain kinematic rotations, which are critical to attitude direction control systems commonly found in vehicles.

About Commensurability of Diversity within and among Communities

(1) Background: Is variation among the communities of a metacommunity higher than within the communities? Community ecologists and population geneticists often characterize the structure of metacommunities by partitioning variation (diversity) into the two following components using measures such as FST or GST and α- and β-diversity. The within-communities component is usually some average of (type, species, genetic) diversities within the communities, and the among-communities component is the additive or multiplicative complement of the overall diversity. Such an among-communities component lacks independent conceptual specification, a matter of long-standing dispute. Only if the two components are independently and commensurably specified can the central question of comparability be answered meaningfully. (2) Methods: A novel approach to overcoming this conceptual weakness identifies two principles of the partitioning of variation among communities (concentration and division) then relates these principles to the common notions of variation (diversity) within and among communities, distinguishes primary indicators to quantify the partitioning principles, transforms the indicators into conceptually independent measures (indices) of variation within and among communities, and by this attains their commensurability and thus comparability. The application of the methods to quantifying the effects of evolutionary mechanisms is outlined. (3) Results: Common approaches are corrected and extended. (a) Analyses of metacommunity/metapopulation structures that rely on apportionment or related indices and take its complement to be differentiation yield incomparable measures of variation within and among communities. (b) The common practice of partitioning the total diversity into additive or multiplicative components produces the inconsistent ranking of the two components. (c) Community concentration and division can result from elementary processes of adaptive differentiation and migration (gene flow) among communities, where the (commensurable) amounts of community concentration and division reflect the relative participation of these processes in metacommunity structuring and translate directly into the measures of diversity within and among communities. (d) The modelling of the contributions of the two partitioning principles to the metacommunity structure is restricted by the marginal distributions of types and community affiliation. (e) The model demonstrates the degree to which adaptational processes at the metacommunity level are mixtures of adaptational events within and among communities.

Fast electron contribution in electronic stopping for p-He and p-Ar collisions

Our study has shown that in collisions p-He and p-Ar with energies above 50 keV fast electrons carry away as kinetic energy up to 70 % of energy released during particle stopping. Ignoring the fast electron contribution makes impossible bringing independently measured cross sections of elementary processes of ionization, excitation, stripping and charge exchange into compliance with measured cross sections of electronic stopping. Fast electron emission in collisions of energetic ions with solids may induce extra radiation effects (create additional vacancies and defects in solid).Mean kinetic energies of ejected electrons We obtained from the analysis of cross section ratio agree well with directly measured energy spectra of the emitted electrons. The dynamic ionization theory implies the We proportionality to initial velocity v. In the considered cases, such a dependence takes place at the velocities below 2 a.u. At higher velocities, the observed dependence is successfully described in the framework of the Born approximation.

Calorimetry of a phase slip in a Josephson junction

Josephson junctions are a central element in superconducting quantum technology; in these devices, irreversibility arises from abrupt slips of the quantum phase difference across the junction. This phase slip is often visualized as the tunnelling of a flux quantum in the transverse direction to the superconducting weak link, which produces dissipation. Here we detect the instantaneous heat release caused by a phase slip in a Josephson junction, signalled by an abrupt increase in the local electronic temperature in the weak link and subsequent relaxation back to equilibrium. Beyond the advance in experimental quantum thermodynamics of observing heat in an elementary quantum process, our approach could allow experimentally investigating the ubiquity of dissipation in quantum devices, particularly in superconducting quantum sensors and qubits.

The role of precursor states in the stereo-dynamics of elementary processes.

The present perspective review focuses on the role of the precursor state, controlling the dynamical evolution of elementary processes, whose structure and stability are often difficult to characterize on quantitative grounds. In particular, such a state depends on the critical balance of weak intermolecular forces operative at long and intermediate separation distances. In this paper, a complementary problem has been properly addressed, concerning the suitable formulation of the intermolecular forces involved, defined in terms of a limited number of parameters and applicable in the whole space of the relative configurations of interacting partners. Important help to the solution of such a problem has been provided by the phenomenological method which adopts semi-empirical and empirical formulas to represent the basic features of the leading interaction components. Such formulas are defined in terms of a few parameters directly or indirectly related to the fundamental physical properties of the interacting partners. In this way, the basic features of the precursor state controlling its stability and its dynamical evolution have been defined in an internally consistent way for several elementary processes, having apparently different natures. Particular attention has been paid to the chemi-ionization reactions: they are treated as prototype oxidation processes for which all electronic rearrangements affecting stability and evolution of the precursor state, coincident with the reaction transition state, have been characterized in great detail. The obtained information appears to be in the perspective of general interest for many other elementary processes, difficult to investigate in the same detail since many other effects mask their basic features.

The High Brilliance neutron Source (HBS): A project for a next generation neutron research facility

The High Brilliance neutron Source (HBS) is a project for a next generation neutron research facility, based on new concepts and recent technological advancements. As elementary processes it uses neither fission nor spallation, but instead low energy nuclear reactions in a very compact Target-ModeratorReflector (TMR) assembly. Our facility design results in very efficient production of neutron beams with high brightness. Key features of HBS are: (i) very competitive instrument performance, (ii) comparatively low construction and operation costs, (iii) resilience, (iv) sustainability, (v) flexibility, (vi) accessibility and (vii) scalability. Here we present the basic layout of the facility, elaborate on the mentioned key features and report on the commissioning of a small test setup.