Theoretical Description Research Articles

Jaynes–Cummings model breaks down when the cavity geometry significantly reduces free-space emission

Strong coupling between a single resonator mode and a single quantum emitter is key to a plethora of experiments and applications in quantum science and technology and is commonly described by means of the Jaynes–Cummings model. Here, we show that the Jaynes–Cummings model only applies when the cavity does not significantly change the emitter’s decay rate into free-space. Most notably, the predictions made by the Jaynes–Cummings model become increasingly wrong when approaching the ideal emitter-resonator systems with no free-space decay channels. We present a Hamiltonian that provides, within the validity range of the rotating wave approximation, a correct theoretical description that applies to all regimes. As minimizing the coupling to free-space modes is paramount for many cavity-based applications, a correct description of strong light-matter interaction is therefore crucial for developing and optimizing quantum protocols.

Damage identification in scale sensitive beam-like nano-joints in the framework of space-fractional Euler–Bernoulli theory

In the paper, a fundamental question about damage identification in scale-sensitive bodies is posed. For this purpose, nano-scale beam-like joints are analyzed using dedicated computational schemes. The theoretical description is led in the framework of non-local space-fractional Euler–Bernoulli (s-FEBB) theory — a special case of space-Fractional Continuum Mechanical model generalizing classical continuum mechanics utilizing fractional calculus. The problem of damage identification is stated as an optimization task where the original numerical strategy is implemented. What is crucial, the s-FEBB model assumes constitutive parameters identified and validated for the silver nanobeam in previous studies. Based on tens of thousands of analyses, we arrive at the general conclusion that localization of fracture/damage/deterioration in material bodies whose dimensions are of the order of intrinsic microstructure is possible but requires advanced modeling — otherwise, damage can be identified in a wrong place or more places, or local damage can become distributed one and/or with wrong intensity.

Effects of delay and reminders on time-based prospective memory in a naturalistic task

ABSTRACT The current study examined the effect of a delay on naturalistic time-based prospective memory (PM) tasks. Two experiments were performed to compare PM performance on a texting task with delays of 1 to 6 days after an initial session. In the first experiment, half of the participants were asked to repeat their response with the same delay to test whether requiring a second response (i.e., a repeated PM task, such as taking medication at the same time each day) would affect time-based PM performance. In the second experiment, participants were given an implicit or an explicit reminder several hours before their time to respond to examine the effect of type of reminder on this PM task. The results of both experiments showed a significant decline in PM performance between the 1-day and multi-day delays. Repeating responses (Experiment 1) had no effect on accuracy of the PM task, but in Experiment 2, explicit experimenter-initiated reminders significantly increased time-based PM performance compared with implicit reminders. These results are discussed in the context of previous studies that have tested delay effects on time-based PM and current theoretical descriptions of time-based PM.

The three-dimensional structure of black hole accretion flows within the plunging region

ABSTRACT We analyse, using new analytical models and numerical general relativistic magnetohydrodynamic simulations, the three-dimensional properties of accretion flows inside the plunging region of black hole spacetimes (i.e. at radii smaller than the innermost stable circular orbit). These simulations are of thick discs, with aspect ratios of order unity $h/r \sim 1$, and with a magnetic field geometry given by the standard low-magnetization ‘SANE’ configuration. This work represents the first step in a wider analysis of this highly relativistic region. We show that analytical expressions derived in the ‘thin disc’ limit describe the numerical results remarkably well, despite the large aspect ratio of the flow. We further demonstrate that accretion within this region is typically mediated via spiral arms, and that the geometric properties of these spiral structures can be understood with a simple analytical model. These results highlight how accretion within the plunging region is fundamentally two-dimensional in character, which may have a number of observational implications. We derive a modified theoretical description of the pressure within the plunging region which accounts for turbulent heating and may be of use to black hole image modelling.

Theoretical description of photoinduced electron transfer in donor-acceptor supramolecular complexes based on carbon buckybowls.

Herein, we explore, from a theoretical perspective, the nonradiative photoinduced processes (charge separation and energy transfer) within a family of donor-acceptor supramolecular complexes based on the electron-donor truxene-tetrathiafulvalene (truxTTF) derivative and a series of curved fullerene fragments (buckybowls) of different shapes and sizes (C30H12, C32H12, and C38H14) as electron acceptors that successfully combine with truxTTF via non-covalent interactions. The resulting supramolecular complexes (truxTTF·C30H12, truxTTF·C32H12, and truxTTF·C38H14) undergo charge-separation processes upon photoexcitation through charge-transfer states involving the donor and acceptor units. Despite the not so different size of the buckybowls, they present noticeable differences in the charge-separation efficiency owing to a complex decay post-photoexcitation mechanism involving several low-lying excited states of different natures (local and charge-transfer excitations), all closely spaced in energy. In this intricate scenario, we have adopted a theoretical approach combining electronic structure calculations at (time-dependent) density functional theory, a multistate multifragment diabatization method, the Marcus-Levitch-Jortner semiclassical rate expression, and a kinetic model to estimate the charge separation rate constants of the supramolecular heterodimers. Our outcomes highlight that the efficiency of the photoinduced charge-separation process increases with the extension of the buckybowl backbone. The supramolecular heterodimer with the largest buckybowl (truxTTF·C38H14) displays multiple and efficient electron-transfer pathways, providing a global photoinduced charge separation in the ultrafast time scale in line with the experimental findings. The study reported indicates that modifications in the shape and size of buckybowl systems can give rise to attractive novel acceptors for potential photovoltaic applications.

Graph Theoretical Description of Phase Transitions in Complex Multiscale Phases with Supramolecular Assemblies.

Phase transitions are typically quantified using order parameters, such as crystal lattice distances and radial distribution functions, which can identify subtle changes in crystalline materials or high-contrast phases with large structural differences. However, the identification of phases with high complexity, multiscale organization and of complex patterns during the structural fluctuations preceding phase transitions, which are essential for understanding the system pathways between phases, is challenging for those traditional analyses. Here, it is shown that for two model systems- thermotropic liquid crystals and a lyotropic water/surfactant mixtures-graph theoretical (GT) descriptors can successfully identify complex phases combining molecular and nanoscale levels of organization that are hard to characterize with traditional methodologies. Furthermore, the GT descriptors also reveal the pathways between the different phases. Specifically, centrality parameters and node-based fractal dimension quantify the system behavior preceding the transitions, capturing fluctuation-induced breakup of aggregates and their long-range cooperative interactions. GT parameterization can be generalized for a wide range of chemical systems and be instrumental for the growth mechanisms of complex nanostructures.

Разрушение дорожного льда сферическим бойком

The article provides a brief overview of the state of the issue of the theoretical description of the process of ice destruction, presents a developed mechanical and mathematical model describing the process of ice destruction by a spherical striker, analyzes the results of calculations based on the obtained formulas for the adequacy of the quantitative assessment of the process. The model is illustrated by a computational scheme of the impact interaction of a striker and a half-space. Empirical correction of theoretical dependencies has been performed. Experimental studies are described, an analysis of their results and the identified conditions of the ice destruction process are presented, as well as the results of empirical correction of theoretical dependencies obtained on their basis, providing a correct quantitative assessment of the process of ice destruction by a spherical striker. The results of an experimental verification of the adequacy of the obtained refined empirical-theoretical dependencies and a method for determining the parameters of a working organ with spherical strikers for breaking ice based on them are presented. The dependences of the results of theoretical and experimental determination of the depth of penetration of the striker rod into the ice are compared. The patterns of crushing of thin ice are revealed depending on the speed of rotation of the rotor, the mass of the inertial strikers and their shape.

Alpha radioactivity deep-underground as a probe of axion dark matter

We propose to investigate the time modulation of radioisotope decays deep underground as a method to explore axion dark matter. In this work, we focus on the α-decay of heavy isotopes and develop a theoretical description for the θ-dependence of α-decay half-lives, which enables us to predict the time variation of α-radioactivity in response to an oscillating axion dark matter background. To probe this scenario, we have recently constructed and installed a setup deep underground at the Gran Sasso Laboratory, based on the α-decay of Americium-241. This prototype experiment, named RadioAxion-α, will allow us to explore a broad range of oscillation's periods, from a micro-second up to one year, thus providing competitive limits on the axion decay constant across 13 orders of magnitude in the axion mass, ranging from 10−9 eV to 10−20 eV after one month of data collection, and down to 10−22 eV after three years.

Emerging Spin-Orbit Torques in Low-Dimensional Dirac Materials.

We report a theoretical description of novel spin-orbit torque components emerging in two-dimensional Dirac materials with broken inversion symmetry. In contrast to usual metallic interfaces where fieldlike and dampinglike torque components are competing, we find that an intrinsic dampinglike torque which derives from all Fermi-sea electrons can be simultaneously enhanced along with the fieldlike component. Additionally, hitherto overlooked torque components unique to Dirac materials emerge from the coupling between spin and pseudospin angular momenta, leading to spin-pseudospin entanglement. These torques are found to be resilient to disorder and could enhance the magnetic switching performance of nearby magnets.

Solidification of Tungsten Inert Gas–Welded Austenitic Stainless Steel with 0.17 wt% N

In this study, an austenitic CrMnNi–N steel is examined with regard to its solidification behavior of the weld metal. For this purpose, the cooling rate of the weld metal at different welding speeds is determined for tungsten inert gas welding without filler metal. The relationship between secondary dendrite arm spacing () and cooling rate () can be described using . Moreover, the microstructure is characterized by a scanning electron microscope using energy‐dispersive X‐ray spectroscopy (EDS). Based on the EDS measurement, it is possible to describe the microsegregation of Cr, Ni, Mn, Mo, and N. The detected microsegregation behavior is compared with the results obtained from Thermo‐Calc calculations. The microsegregation varies depending on the present phase during solidification and correlate well with microstructure observations. By using the software Thermo‐Calc, the theoretical description of solidification is based on the classical Scheil model with fast diffusion of N. A primary ferritic solidification is calculated, which correlates with the experimental findings.

Алгоритм планирования маршрута БПЛА в условиях недостатка визуальных ориентиров

Today, unmanned aircraft is used to solve a variety of tasks. One of the problems that arise when using unmanned aerial vehicles (UAVs) is the problem of navigation, in particular, determining their exact location in space. Today, there are various methods to solve this problem. A promising way to solve it in conditions where it is impossible to use a satellite navigation system is video navigation systems that use visual landmarks to determine location. In this paper, an overview of the existing types of UAV video navigation systems was carried out. The peculiarities of the operation of video navigation systems using the comparison of visual landmarks with satellite maps were also highlighted. The task was set to find a route in conditions of a lack of visual landmarks, in which the problem of losing reference points may arise. The graph data format used is described, which stores the values of the metric of the diversity of the underlying surface, which characterizes the magnitude of the probability of the problem of losing reference points. The existing algorithms for finding a path in a graph are considered and the need to develop a new algorithm is justified. A theoretical description of the algorithm was proposed, in which the path search process is divided into two stages: first, a solution option is searched for with the maximum value of the metric of diversity of the underlying surface, and then a route with the minimum length is selected. Several options of the implementation of the proposed algorithm were also presented and their asymptotic complexity was estimated. Based on the theoretical description, a software implementation of the proposed algorithm was developed and an experimental verification of the correctness of its operation on a test card with various flight tasks was performed. According to the test results, the proposed algorithm has shown its effectiveness by constructing routes correctly in all test examples. In the future, this algorithm can be used as part of the UAV video navigation system. The main advantages and disadvantages of the proposed algorithm were also described and ways for its further improvement were proposed.

Evolutionary dynamics of any multiplayer game on regular graphs

Multiplayer games on graphs are at the heart of theoretical descriptions of key evolutionary processes that govern vital social and natural systems. However, a comprehensive theoretical framework for solving multiplayer games with an arbitrary number of strategies on graphs is still missing. Here, we solve this by drawing an analogy with the Balls-and-Boxes problem, based on which we show that the local configuration of multiplayer games on graphs is equivalent to distributing k identical co-players among n distinct strategies. We use this to derive the replicator equation for any n-strategy multiplayer game under weak selection, which can be solved in polynomial time. As an example, we revisit the second-order free-riding problem, where costly punishment cannot truly resolve social dilemmas in a well-mixed population. Yet, in structured populations, we derive an accurate threshold for the punishment strength, beyond which punishment can either lead to the extinction of defection or transform the system into a rock-paper-scissors-like cycle. The analytical solution also qualitatively agrees with the phase diagrams that were previously obtained for non-marginal selection strengths. Our framework thus allows an exploration of any multi-strategy multiplayer game on regular graphs.

Hidden transport phenomena in an ultraclean correlated metal

Advancements in materials synthesis have been key to unveil the quantum nature of electronic properties in solids by providing experimental reference points for a correct theoretical description. Here, we report hidden transport phenomena emerging in the ultraclean limit of the archetypical correlated electron system SrVO3. The low temperature, low magnetic field transport was found to be dominated by anisotropic scattering, whereas, at high temperature, we find a yet undiscovered phase that exhibits clear deviations from the expected Landau Fermi liquid, which is reminiscent of strange-metal physics in materials on the verge of a Mott transition. Further, the high sample purity enabled accessing the high magnetic field transport regime at low temperature, which revealed an anomalously high Hall coefficient. Taken with the strong anisotropic scattering, this presents a more complex picture of SrVO3 that deviates from a simple Landau Fermi liquid. These hidden transport anomalies observed in the ultraclean limit prompt a theoretical reexamination of this canonical correlated electron system beyond the Landau Fermi liquid paradigm, and more generally serves as an experimental basis to refine theoretical methods to capture such nontrivial experimental consequences emerging in correlated electron systems.

Phase-field model of glass transition: behavior under uniform quenching

ABSTRACT The process of transition from the liquid to the solid state during the uniform quenching is described by a combination of two theoretical approaches: the phase field method and the gauge theory, which suggests the phase transition in the subsystem of topologically stable distortions. Using the stochastic partial differential equations we numerically simulate competition between the processes of crystallization and vitrification during the rapid cooling of the melt. A glass order parameter which is suitable for the characterization of transition to the glassy state has been proposed. At low cooling rates, the domain freezes into the crystalline structure with defects, and its glass order parameter is orders of magnitude less than that for the vitrified state obtained by rapid quenching. Proposed method improves and extends the theoretical description of glass transition, qualitatively represents the basic kinetic properties of the process and demonstrates sensitivity of resulting microstructures to the quenching rate.

Algorithm for forming a set of indicators of international trade customs regulation effectiveness in the EAEU member states

The relevance of the study is due to the fact that international trade globalization and intensification increase competitiveness of not only domestic but also foreign producers, so the business sector expects to facilitate business conditions, simplify customs procedures, increase customs activities efficiency, and improve customs services provision. Goods transportation across the customs borders of countries around the world presents challenges in filling out documentation, transportation methods, information processing, and compliance with regulations that are not internationally harmonized. It leads to customs laws violations that must be detected during the customs control process. Consequently, customs regulation effectiveness will depend directly on the customs control results. The article presents a theoretical and methodological description of the procedure for assessing international trade customs regulation effectiveness in the EAEU member states, as well as a vector for developing a comprehensive set of performance indicators. The proposed assessment algorithm and the set of quantitative and qualitative indicators can be regarded as fundamental interrelated criteria that ensure improvement of efficiency of control over the customs authorities’ activities and corrective management decisions, if necessary. The application in customs practice of the proposed indicators for assessing international trade customs regulation effectiveness will contribute to customs policy effective implementation for the harmonious development of the EAEU member states’ economies, including Russia, in modern society and the basis of their sustainable political, economic and social development.

Democracy: a modern definition for the library field

PurposeDue to contemporary threats to democracy, the topic is highly prominent in news and social discourse. The Library and Information Science (LIS) field writes about democracy frequently and it is a core concept underwriting many common library practices, but it lacks a working definition of modern democracy. This article supplies a minimal definition of democracy specifically for LIS, and expands the concept to encompass a more empirically accurate concept of library roles in democratic societies that includes the sociology of democracy where libraries arguable play a more significant role.Design/methodology/approachThere is an unpacking of library assumptions about operating in democratic societies, an empirical survey of the conditions of modern democracy, and a baseline theoretical description of democratic functioning as it currently exists.FindingsA minimal definition of modern democracy situates library practices – and in some ways minimizes them. However, the role of culture – the sociology that democracy presumes – comes to prominence when the civil society role of libraries and the conditions of successful democratic functioning are examined.Originality/valueThere is now a minimal definition of democracy for LIS with this effort, but it needs expansion. In that sense, LIS is a leading example of the undertheorized role of the sociology that democracy presumes.

The self-of-therapist: a new task for Emotion-focused Therapy supervision

ABSTRACT In emotion-focused therapy (EFT), it is not uncommon for therapists to experience intrusive therapist reactions (ITR) to their work with clients, interfering with their therapeutic focus and the provision of Rogerian core conditions. The EFT supervision manual suggests supervisors continuously monitor supervisee reactions and offer guided exploration of what has arisen. The presence of an ITR as a significant event in supervision indicates a marker to perform self-of-therapist work. This study presents a theoretical description of the stages of a new supervision task called the self-of-therapist (SOT) for working with ITRs in EFT supervision. Responding to ITRs and performing SOT work is viewed as critical for the development of EFT therapists. The SOT concept is defined and an EFT, process-oriented conceptualization of SOT is provided. The structure of the task is outlined, and case illustrations are provided. Future steps are then outlined for the task’s further development.

Entanglement transition and heterogeneity in long-range quadratic Lindbladians

The generation of entanglement in mixed states is relevant to quantum systems coupled to an environment. The dissipative and mixing properties of the environment are unavoidable in physical platforms for quantum simulation and information processing, where entanglement can be a vital resource. In this work, we explore entanglement and heterogeneity in random Lindbladian dynamics describing open quantum systems. We propose a model of a one-dimensional chain of noninteracting, spinless fermions coupled to a local ensemble of baths. The jump operator mediating the interaction with the bath linked to each site has a power-law tail with an exponent p. We show that the system undergoes volume-to-area law entanglement phase transition in the mixed steady state by tuning p which remains stable in the presence of coherent hopping. Unlike the entanglement transition in the pure-state quantum trajectories of open systems, this transition is exhibited by the averaged steady-state density matrix of the Lindbladian. The steady state in the area-law phase is characterized by a spatial heterogeneity in local population imbalance, while the jump operators exhibit a constant participation ratio of the sites they affect. Our work provides a theoretical description of an entanglement transition realized in long-ranged open quantum systems and provides an avenue to stabilize quantum correlations in mixed states. Published by the American Physical Society 2024

Polymer-dispersed liquid-crystal coatings for ultrasound visualization: Experiment and theory.

Polymer dispersed liquid crystal (PDLC) films are formed of droplets of liquid crystal (LC) held in a polymer matrix. Similar to aligned LC films, PDLCs exhibit the acousto-optic (AO) effect when excited by acoustic waves of sufficient amplitude, whereby the PDLC film becomes transparent in the excited regions (acoustic clearing). Despite decades of research there is still debate over the mechanisms of the AO effect for the case of LC films, with several competing theories, and AO effects in PDLC have not been studied theoretically. This paper explores the AO effect in PDLC both experimentally and theoretically, and attempts a theoretical description of the observed phenomena based on the theoretical approach by Selinger etal. for aligned LC films. The acousto-optic effect in PDLC is shown to be due to direct interaction of acoustic waves with LC droplets, rather than due to compression of the droplet itself. Polarizing microscopy revealed changes in droplet shape at excited points. This is consistent with reorientation as a contributing factor, possibly coexisting with flows at higher excitation powers. In previous experimental studies PDLC films were prepared with cover slides, in the same way as LC AO cells, significantly limiting applications by adding complexity to the design. Also, to exhibit AO clearing it was considered that the PDLC needed to be prepared with high LC concentrations (over 75% by weight). We demonstrate that no cover slide is necessary, and that PDLC coatings without a cover have improved sensitivity to acoustic waves. We demonstrate the AO effect for LC concentrations as low as 40% by weight. The ability to use standard composition PDLC, with no top cover, is paving the way to paint-on visual ultrasound sensors.

Spreading and Capillary Imbibition of Viscous Oil Lens into an Open-Cell Porous Structure.

Oil pollution in the ocean is becoming more and more of a serious issue, which increases interest in both ways for combating its cause and methods for observing and monitoring how oil spreads. A promising approach based on an optical method with empirical relations for selected viscous oil-water systems is presented. Based on a modified melamine sponge (MMS), the microscopic spreading and oil capillary penetration phenomenon of the porous structure were investigated. The objective of this study is 2-fold: (i) to present a more thorough experimental description of the spreading of viscous oil lens on the water surface and capillary action of oil lens into MMS porous structure; and (ii) to provide a theoretical description that helps to explain some of the observed behavior. With knowledge of , we can determine the spreading coefficient S. It needs to be pointed out that the oil lens floating on the water surface does satisfy Neumann's rule as the spreading coefficient of the air-oil-water system is negative (- 9.8 mN/m), indicating the ability to form a stable oil lens with thickness δO = 3.04 mm and radius RL = 38.64 mm after 60 min of spreading test. Furthermore, to better understand the capillary phenomena from a mechanical approach, an oil lens in contact with the surface of the MMS porous structure, by in-depth visualization, is properly defined as the balance of forces acting. Finally, as an illustration of this method, we utilized this approach to obtain the equilibrium height of the capillary rise and take it into account in terms of effective material thickness.