Quasi-stationary State Research Articles

Electronic states bound by repulsive potentials in graphene irradiated by a circularly polarized electromagnetic field.

In the framework of the Floquet theory of periodically driven quantum systems, it is demonstrated that irradiation of graphene by a circularly polarized electromagnetic field induces an attractive area in the core of repulsive potentials. Consequently, the quasi-stationary electron states bound by the repulsive potentials appear. The difference between such field-induced states in graphene and usual systems with the parabolic dispersion of electrons is discussed and possible manifestations of these states in electronic transport and optical spectra of graphene are considered.

Transient dielectric function dynamics driven by coherent phonons in Bismuth crystal

In this study, we investigate the transient dynamics of the dielectric function in photoexcited bismuth using a double-probe experiment. We demonstrate how the A1g coherent phonon mode influences both the real and imaginary components of the dielectric function, extending to a quasi-steady state. Additionally, we compare this transient behavior to ellipsometry measurements taken at varying crystal temperatures under equilibrium conditions. Our findings reveal that bismuth crystals, when excited by femtosecond laser pulses, enter a quasi-stationary state that follows the coherent phonon oscillations. This transient state is distinct from a liquid phase or a simple thermalized state. We interpret this quasi-steady state as a heated, excited state where electron-hole recombination has not yet occurred.

Modeling the structure changes of cold-water copepods Calanus euxinus population under the influence of the black sea depths deoxygenation

The paper presents the results of modeling the possible changes in the structure of the population of Calanus euxinus Hulsemann, 1991 copepods in the Black Sea under the influence of deoxygenation that began in the late 1980s. Over the past 50 years, the depth of oxygen penetration in the deep sea has decreased by almost 50 m. The lower “life limit” of zooplankton in the Black Sea corresponds to the upper boundary of the suboxic layer, where intense copepod aggregation occurs at an oxygen concentration of 10 μM /L. In 1955–1976, this boundary was 130–140 m across the sea, but due to eutrophication and climate change since late 1980s, it has risen in deep water areas to 70–80 m. As a result, the dense copepod layers near the redoxcline and especially their reserve population stock, consisting of non-migrating individuals in diapause, may have been subjected to intensive eating by the Black Sea sprat, which lives to a depth of 100 m and can tolerate hypoxia. To explore this process, we created a new population dynamics model for C. euxinus, which makes it possible to assess changes in the abundance and structure of the population under conditions of a quasi-stationary state and during intensive predation of individuals in diapause. The model describes the dynamics of the Сalanus population based on a statistical description of the relationship between the growth of individuals, their fecundity, the duration of diapause, mortality, and environmental conditions: the concentration of food suspension and temperature in the layer of vertical migration. We put forward the hypothesis that the access of small pelagic fish to the concentration layers of copepods in diapause has a key effect on significant changes in the Black Sea ecosystem, associated with a decrease in the supply of forage plankton and fluctuations in the abundance of pelagic fish.

On the Formation of a Quasi-stationary Non-Traveling cluster in the Attractive Hamiltonian Mean-Field Model

Abstract Long-range interacting systems usually exhibit quasi-stationary states that deviate from thermal equilibrium over extended periods of time. In particular, in the attractive Hamiltonian mean-field (HMF) model, one of these states is characterized by traveling clusters of particles in the phase-space, generated by the resonance with two counter-propagating density waves. Here, we report the existence of a third, non-traveling cluster, and we explain its formation by the existence of a stationary wave in the system which is generated as a product of a linear superposition of the other two counter-propagating waves.

CryoTRANS: predicting high-resolution maps of rare conformations from self-supervised trajectories in cryo-EM

Cryogenic electron microscopy (cryo-EM) has revolutionized structural biology, enabling efficient determination of structures at near-atomic resolutions. However, a common challenge arises from the severe imbalance among various conformations of vitrified particles, leading to low-resolution reconstructions in rare conformations due to a lack of particle images in these quasi-stable states. We introduce CryoTRANS, a method that predicts high-resolution maps of rare conformations by constructing a self-supervised pseudo-trajectory between density maps of varying resolutions. This trajectory is represented by an ordinary differential equation parameterized by a deep neural network, ensuring retention of detailed structures from high-resolution density maps. By leveraging a single high-resolution density map, CryoTRANS significantly improves the reconstruction of rare conformations and has been validated on four real-world datasets: alpha-2-macroglobulin, actin-binding protein complexes, SARS-CoV-2 spike glycoprotein, and the 70S ribosome. CryoTRANS can also predict high-resolution structures in cryogenic electron tomography maps using a high-resolution cryo-EM map.

Numerical simulations of temperature anisotropy instabilities stimulated by suprathermal protons

The new in situ measurements of the Solar Orbiter mission contribute to the knowledge of the suprathermal populations in the solar wind, especially of ions and protons whose characterization, although still in the early phase, seems to suggest a major involvement in the interaction with plasma wave fluctuations. Recent studies point to the stimulating effect of suprathermal populations on temperature anisotropy instabilities in the case of electrons already being demonstrated in theory and numerical simulations. Here, we investigate anisotropic protons, addressing the electromagnetic ion-cyclotron (EMIC) and the proton firehose (PFH) instabilities. Suprathermal populations enhance the high-energy tails of the Kappa velocity (or energy) distributions measured in situ, enabling characterization by contrasting to the quasi-thermal population in the low-energy (bi-)Maxwellian core. We use hybrid simulations to investigate the two instabilities (with ions or protons as particles and electrons as fluid) for various configurations relevant to the solar wind and terrestrial magnetosphere. The new simulation results confirm the linear theory and its predictions. In the presence of suprathermal protons, the wave fluctuations reach increased energy density levels for both instabilities and cause faster and/or deeper relaxation of temperature anisotropy. The magnitude of suprathermal effects also depends on each instability's specific (initial) parametric regimes. These results further strengthen the belief that wave-particle interactions govern space plasmas. These provide valuable clues for understanding their dynamics, particularly the involvement of suprathermal particles behind the quasi-stationary non-equilibrium states reported by in situ observations.

Tunnel transport problem for open multilayer nitride nanostructures with an applied constant magnetic field and time-dependent potential: An exact solution

A quantum mechanical theory for description of electronic quasistationary states in two-dimensional (2D) layered semiconductor nanostructure was developed. A constant external magnetic field B was directed along semiconductor layers. The presence of internal electric fields F originated from the potential barriers and wells in semiconductor layers was taken into account. The vector of F was directed perpendicularly to semiconductor layers. The interaction of tunneled electrons with a time-dependent electromagnetic fields was analyzed in detail. An approach to obtain an exact solution to the problem based on a combination of the Lewis-Riesenfeld method for complete Schrödinger equation and scattering theory was developed. Application of the scattering theory in combination with the -matrix and transfer-matrix methods allowed us to calculate the electron quasistationary spectra. Effects of magnetic field on the resonant energy and width of electronic quasistationary states as well as on the electronic conductivity were also discussed. Published by the American Physical Society 2024

Hydrodynamic simulation of Cygnus OB2: the absence of a cluster wind termination shock

ABSTRACT We perform a large-scale hydrodynamic simulation of a massive star cluster whose stellar population mimics that of the Cygnus OB2 association. The main-sequence stars are first simulated during 1.6 Myr, until a quasi-stationary state is reached. At this time, the three Wolf–Rayet stars observed in Cygnus OB2 are added to the simulation, which continues to 2 Myr. Using a high-resolution grid in the centre of the domain, we can resolve the most massive stars individually, which allows us to probe the kinetic structures at small (parsec) scales. We find that, although the cluster excavates a spherical ‘superbubble’ cavity, the stellar population is too loosely distributed to blow a large-scale cluster wind termination shock, and that collective effects from wind–wind interactions are much less efficient than usually assumed. This challenges our understanding of the ultra-high energy emission observed from the region.

A Semi-Continuous Fermentation Process for Pulque Production Using Microfiltration-Sterilized Aguamiel and Aseptic Conditions to Standardize the Overall Quality of the Beverage

Despite the current appreciation of pulque as a probiotic fermented beverage, pulque has been also regarded as a poor-quality product, particularly due to the lack of sanitary control during its elaboration. To address this problem, a semi-continuous fermentation system was established, emulating the artisanal production process. Microfiltration-sterilized aguamiel was employed as the substrate, whereas a good-quality pulque was used as the fermentation inoculum. During the fermentation, the physicochemical, microbiological (lactic acid and Leuconostoc-type bacteria and yeasts) and sensory characteristics of the must were monitored. The isolated microorganisms were identified by molecular biology and MALDI-MS techniques. The sterilization of aguamiel by microfiltration did not negatively affect its physicochemical attributes. After 6–8 days of operation of the semi-continuous bioreactor, the fermentation reached a quasi-stationary state considering most of the parameters monitored during the experiment. The final fermentation product presented similar physicochemical, microbial and sensory properties to those of the pulque inoculum. The genera identified were Leuconostoc, Lentilactobacillus, Lactobacillus, Liquorilactobacillus, Fructilactobacillus and Saccharomyces. The strains Lentilactobacillus diolivorans and Liquorilactobacillus capillatus and uvarum have not been previously isolated from pulque. In conclusion, the fermentation system developed in this work was effective to standardize the quality of pulque while preserving the positive attributes of the artisanal process, thus harnessing the probiotic properties of pulque.

Implications of Using Scalar Forcing to Sustain Reactant Mixture Stratification in Direct Numerical Simulations of Turbulent Combustion

A recently proposed scalar forcing scheme that maintains the mixture fraction mean, root-mean-square and probability density function in the unburned gas can lead to a statistically quasi-stationary state in direct numerical simulations of turbulent stratified combustion when combined with velocity forcing. Scalar forcing alongside turbulence forcing leads to greater values of turbulent burning velocity and flame surface area in comparison to unforced simulations for globally fuel-lean mixtures. The sustained unburned gas mixture inhomogeneity changes the percentage shares of back- and front-supported flame elements in comparison to unforced simulations, and this effect is particularly apparent for high turbulence intensities. Scalar forcing does not significantly affect the heat release rates due to different modes of combustion and the micro-mixing rate within the flame characterised by scalar dissipation rate of the reaction progress variable. Thus, scalar forcing has a significant potential for enabling detailed parametric studies as well as providing well-converged time-averaged statistics for stratified-mixture combustion using Direct Numerical Simulations in canonical configurations.

Violent relaxation in one-dimensional self-gravitating system: Deviation from the Vlasov limit due to finite-N effects.

We investigate the effect of a finite particle number N on the violent relaxation leading to the quasistationary state (QSS) in a one-dimensional self-gravitating system. From the theoretical point of view, we demonstrate that the local Poissonian fluctuations embedded in the initial state give rise to an additional term proportional to 1/N in the Vlasov equation. This term designates the strength of the local mean-field variations by fluctuations. Because it is of the mean-field origin, we interpret it differently from the known collision term in the way that it effects the violent relaxation stage. Its role is to deviate the distribution function from the Vlasov limit, in the collisionless manner, at a rate proportional to 1/N while the violent relaxation is progressing. This hypothesis is tested by inspecting the QSSs in simulations of various N. We observe that the core phase-space density can exceed the limiting density deduced from the Vlasov equationand its deviation degree is in accordance with the 1/N estimate. This indicates the deviation from the standard mean-field approximation of the violent relaxation process by that 1/N term. In conclusion, the finite-N effect has a significant contribution to the QSS apart from that it plays a role in the collisional stage that takes place long after. The conventional collisionless Vlasov equationmight not be able to describe the violent relaxation of a system of particles properly without the correction term of the local finite-N fluctuations.

Quasistationary and stationary electron quantum-confined states in the germanium/silicon nanosystems with germanium quantum dots

This mini-review examines the optical properties of nanoheterostructures of the second type, consisting of germanium quantum dots expressed in a silicon matrix. It has been shown that the radiation intensities and the lifetimes associated with electron transitions between quasistationary states of a single germanium quantum dot, take significant values compared to similar values in germanium/silicon nanosystems. This effect will make it possible to create a new generation of efficient light-emitting devices based heterostructures with germanium quantum dots. In addition, long-lived quasistationary states will make it possible to realize high-temperature quantum Bose-gases states in the nanosystem under study.

Properties of spectral characteristics of quasi-stationary electron states in an open multi-cascade nanostructure

The exact expressions for scattering matrix and transmission coefficient in open multi-cascade nanostructure are obtained. The theory of spectral characteristics of electron quasi-stationary states is developed in two approaches. For the nanostructure with GaAs wells and AlGaAs barriers, it is established that resonance bands appear in the N-cascade structure. Each one is formed by the energies of N states. Only the scattering matrix allows to unambiguously determine the resonance energies and resonance widths of all electron states in the multi-cascade structure. The approach of transmission coefficient, due to the collapse of resonances, gives the incomplete information about the spectral characteristics.

A large population of neutron star low-mass X-ray binaries with long outburst recurrence time?

ABSTRACT Low-mass X-ray binaries (LMXBs) with neutron stars show quite different features that depend on the rate of mass transfer from the donor star. With a high transfer rate, the Z sources are in a persistent soft spectral state, and with a moderate transfer rate the transient Atoll sources have outburst cycles like the black hole X-ray binaries. The observations document very long outburst recurrence times for quite a number of sources. We follow with our computations the evolution of the accretion disc until the onset of the ionization instability. For sources with a low mass transfer rate, the accumulation of matter in the disc is essentially reduced due to the continuous evaporation of matter from the disc to the coronal flow. Different mass transfer rates result in nearly the same amount of matter accumulated for the outburst, which means that the outburst properties are similar for sources with short outburst cycles and sources with long outburst cycles, contrary to some expectations. Then, for systems with long recurrence time, less sources will be detected and the total population of LMXBs could be larger than it appears. This would relieve the apparent problem that the observed number of LMXBs as progenitors of millisecond pulsars (MSPs) is too small compared to the number of MSPs. Concerning the few quasi-persistent sources with year-long soft states, we argue that these states are not outbursts, but quasi-stationary hot states as in Z sources.

Prethermalization in an open quantum system coupled to a spatially correlated bosonic bath

A nearly-integrable isolated quantum many-body system reaches a quasi-stationary prethermal state before a late thermalization. Here, we revisit a particular example in the settings of an open quantum system (OQS). We consider a collection of non-interacting atoms coupled to a spatially correlated bosonic bath characterized by a bath correlation length. Our result implies that the integrability of the system depends on such a correlation length. If this length is much larger than the distance between the atoms, such a system behaves as a nearly-integrable OQS. We study the properties of the emerging prethermal state for this case, i.e. the state’s lifetime, the extensive number of existing quasi-conserved quantities, the emergence of the generalized Gibbs state, and the scaling of von Neumann entropy, etc. We find that for the prethermal state, the maximum growth of entropy is logarithmic with the number of atoms, whereas such growth is linear for the final steady state, which is the Gibbs state in this case. Finally, we discuss how such prethermal states can have significant applications in quantum entanglement storage devices.

Exploring the Differences in Kinetic Energy Spectra between the NCEP FNL and ERA5 Datasets

Abstract Two global atmospheric circulation datasets (ERA5 and NCEP FNL) with horizontal resolutions of 0.25° × 0.25° are investigated in terms of kinetic energy (KE) spectra at 200 hPa (roughly between 11 and 12 km). The horizontal KE (HKE) in NCEP FNL is larger and flatter than that in ERA5 at subsynoptic scales and mesoscales. Restoring the energy of this wavenumber range to the physical space shows that the HKE in NCEP FNL is larger than that in ERA5 over most areas but smaller mainly in the Indo-Pacific warm pool. The spectral budgets show that at these scales, the positive contribution from net vertical flux in ERA5 is stronger than that in NCEP FNL, while the negative contribution from available potential energy (APE) conversion is smaller; assuming that the atmosphere is in a quasi-stationary state, more dissipation is found in ERA5 than in NCEP FNL, which should be responsible for the HKE spectrum in ERA5 to be steeper and weaker than that in NCEP FNL. Our formulation shows that the APE conversion and net vertical flux are related to the pressure vertical velocity (PVV). The APE conversion and net vertical flux differences between the two datasets, like the PVV difference, are mainly from the tropical region. At large scales, the vertical motion in ERA5 is larger than that in NCEP FNL. The amplitude differences of the PVV spectra between two datasets are consistent with those of the large-scale precipitation spectra associated with microphysics parameterizations. These results support that vertical motion is a key dynamical factor explaining energy discrepancies at mesoscales. Significance Statement The atmospheric kinetic energy spectrum reflects energy distribution characteristics in atmospheric motion at different scales. According to the Helmholtz decomposition, the horizontal wind field can be decomposed into two parts: rotational wind field and divergent wind field. We explore the dynamical causes of the atmospheric energy spectra differences among different datasets from the perspective of rotational and divergent components of motion. Our results reveal that the differences in energy spectra and their energy budget at scales below a few hundred kilometers are relatively significant in tropical regions and are closely related to vertical motion. A better understanding of the differences in kinetic energy spectra will contribute to the improvement of atmospheric models.

Effect of Ladle Shroud Blockage on Flow Dynamics and Cleanliness of Steel in Coupled Ladle–Shroud–Tundish System

Herein, a numerical simulation of the coupled ladle–shroud–tundish system is developed in the emptying stage of the ladle toward the tundish to analyze the effect of the obstruction of the shroud clogging on the fluid dynamics pattern, the thermal behavior, and the removal of inclusions. The thermal stratification of steel in a 150 ton ladle is analyzed during the holding period; subsequently, the ladle emptying to a two‐stranded tundish is carried out considering the average temperature at the end of the holding time, and two considerations are made: the first with the shroud utterly free of obstruction and the second with the shroud partially clogged. Finally, alumina particles are added into the tundish once the quasistable state is reached, and their trajectories are simulated using the discrete‐phase model. The steel temperature during the emptying process is compared against temperature measurements reported by the industrial process, showing a decrease of 0.5 K min−1. The results show that the clogging has little influence on the fluid dynamics structure in the ladle; however, it completely modifies the fluid dynamics and temperature distribution in the tundish, decreasing its efficiency for removing inclusions by up to ≈25% for particles of 10 μm.

A Unified Model for Multiepoch Neutrino Events and Broadband Spectral Energy Distribution of TXS 0506+056

The blazar TXS 0506+056 has been proposed as a high-energy neutrino emitter. However, it has been shown that the standard one-zone model cannot produce sufficiently high neutrino flux due to constraints from the X-ray data, implying more complex properties of the radiation zones in the blazar than that described by the standard one-zone model. In this work, we investigate multiepoch high-energy muon-neutrino events associated with the blazar TXS 0506+056 that occurred in 2014–2015, 2017–2018, 2021–2022, and 2022–2023, respectively. We applied the so-called “stochastic dissipation model” to account for the neutrino-blazar associations detected in the four epochs simultaneously. This model describes a scenario in which the emission of the blazar arises from the superimposition of two components: a persistent component related to the quasi-stable state of the blazar and a transient component responsible for the sudden enhancement of the blazar’s flux, either in electromagnetic radiation or in neutrino emission. The latter component could form at a random distance along the jet by a strong energy dissipation event. Under such an assumption, the multiepoch broadband spectral energy distribution can be well explained, and the expected number of high-energy neutrino events is statistically realistic. The expected number of neutrino events in half year is around 8.2, 0.07, 0.73, and 0.41, corresponding to the epoch in 2014–2015, 2017–2018, 2021–2022, and 2022–2023, respectively. Hence, our model self-consistently explains the episodic neutrino emission from TXS 0506+056.

Magnetic properties of NdFeB-based alloy under high-pressure torsion

Abstract When a multicomponent NdFeB-based magnetic alloy is deformed using high-pressure torsion (HPT), a quasi-stationary state is reached after 2.5 anvil revolutions, which corresponds to an equivalent strain of ∼40 at the sample mid-radius. In this state, torque self-oscillations are observed with a period of about 1.5 s and an amplitude of ∼10 % around the average value of 550 N m−1. Such self-oscillations are accompanied by strong acoustic emission. Before HPT, the alloy under study has an almost rectangular hysteresis loop with saturation magnetization J s = 135 emu g−1 and coercivity H c = 34.8 kOe. HPT deformation at initial stages transforms this alloy to the class of soft magnets: H c drops to 1.35 × 10−4 kOe, while J s practically does not change. An increase in strain leads to a gradual increase in H c to 9.61 kOe and a decrease in J s to ∼100 emu g−1 at the number of anvil revolutions n = 7. This is explained by HPT modification of the regular grain-boundary network of neodymium-rich paramagnetic phase layers. These layers provide magnetic isolation between grains of the Nd2Fe14B ferromagnetic phase. Periodic changes in torque and J s with increasing torsion angle are caused by transitions from the amorphous phase to the crystalline one and vice versa.

SIMULATION OF CAPILLARY WAVE TURBULENCE ON THE BASIS OF FULLY NONLINEAR PLANE-SYMMETRIC MODEL

A new model for the direct numerical simulation of capillary wave turbulence arising at a free surface of deep incompressible fluid is proposed in the work. The plane-symmetric model based on the time-dependent conformal transform is fully nonlinear and takes into account the effects of surface tension, external random forcing and dissipation of energy. The simulation results show that the system of nonlinear capillary waves can go into a quasi-stationary state (wave turbulence regime), when the action of an external force is compensated by the viscosity. In this regime, the fluid motion demonstrates quite complex and irregular behavior. The spatial and frequency spectra of surface perturbations acquire a power-law dependence in the quasi-stationary state. The exponents of the spectra do not coincide with the classical Zakharov-Filonenko spectrum obtained for isotropic capillary turbulence. In the case of anisotropic quasi-1D geometry, five-wave resonant interactions become the dominant process. The numerical results agree with high accuracy with the corresponding analytical spectra obtained on the basis of dimensional analysis of weak turbulence spectra.