Strong-coupling Model Research Articles

Parameter Adaptive Terminal Sliding Mode Control of Flexible Coupling Air-Breathing Hypersonic Vehicle

The highly nonlinear and coupling characteristics of a flexible air-breathing hypersonic vehicle create great challenges to its flight control design. A unique parameter adaptive nonsingular terminal sliding mode method is proposed for longitudinal control law design of a flexible coupling air-breathing hypersonic vehicle. This method uses adaptive reaching law gain instead of the additional adaptive compensation term to handle the uncertainty to improve robustness. The stability of the close loop system is proved via a Lyapunov way. The longitudinal tracking control law for velocity and angle of attack is designed based on a rigid dynamic model of a flexible air-breathing hypersonic vehicle. A strong coupling model of the same vehicle, considering aerodynamic-scramjet engine-flight dynamic-elastic couplings, is established as the verification platform of the designed control law. The remarkable differences of flight dynamic characteristics between this strong coupling model and the rigid body model can be seen, which mean the controller needs to endure very great uncertainty, unmodeled dynamics, and other types of internal disturbance. Simulation results based on the coupling model demonstrate that the designed control law has good performance and acceptable robustness.

Effective mass of strong-coupling polaron in polar slab considering the Rashba effect induced by LLP method

On the basis of Huybrechts’ strong-coupling polaron model, the Tokuda modified linear-combination operator method and the unitary transformation method were used to study the properties of the strong-coupling polaron in a polar slab considering the influence of the Rashba effect, which is caused by the spin–orbit interaction, with the triangular quantum well. Numerical calculation on the KCl, as an example, is performed. The expression for the effective mass(m±*) of the polaron as a function of the slab thickness (d), the velocity (u), and the coupling constant (α) was derived. Numerical results show that the interactions between the orbit and the spin with different directions have different effects on the m±* of the polaron.

Behavior of the Energy Spectrum and Electric Conduction of Doped Graphene.

We consider the effect of atomic impurities on the energy spectrum and electrical conductance of graphene. As is known, the ordering of atomic impurities at the nodes of a crystal lattice modifies the graphene spectrum of energy, yielding a gap in it. Assuming a Fermi level within the gap domain, the electrical conductance diverges at the ordering of graphene. Hence, we can conclude about the presence of a metal–dielectric transition. On the other hand, for a Fermi level occurring outside of the gap, we see an increase in the electrical conductance as a function of the order parameter. The analytic formulas obtained in the Lifshitz one-electron strong-coupling model, describing the one-electron states of graphene doped with substitutional impurity atoms in the limiting case of weak scattering, are compared to the results of numerical calculations. To determine the dependence of the energy spectrum and electrical conductance on the order parameter, we consider both the limiting case of weak scattering and the case of finite scattering potential. The contributions of the scattering of electrons on a vapor of atoms to the density of states and the electrical conductance of graphene with an admixture of interstitial atoms are studied within numerical methods. It is shown that an increase in the electrical conductance with the order parameter is a result of both the growth of the density of states at the Fermi level and the time of relaxation of electron states. We have demonstrated the presence of a domain of localized extrinsic states on the edges of the energy gap arising at the ordering of atoms of the admixture. If the Fermi level falls in the indicated spectral regions, the electrical conductance of graphene is significantly affected by the scattering of electrons on clusters of two or more atoms, and the approximation of coherent potential fails in this case.

Peccei-Quinn phase transition at LIGO

The LIGO observatories can potentially detect stochastic gravitational waves arising from phase transitions which happened in the early universe at temperatures around T ∼ 108 GeV. This provides an extraordinary opportunity for discovering the phase transition associated with the breaking of the Peccei-Quinn symmetry, required in QCD axion models. Here we consider the simplest Peccei-Quinn models and study under which conditions a strong first-order phase transition can occur, analyzing its associated gravitational wave signal. To be detectable at LIGO, we show that some supercooling is needed, which can arise either in Coleman-Weinberg-type symmetry breaking or in strongly-coupled models. We also investigate phase transitions that interestingly proceed by first breaking the electroweak symmetry at large scales before tunneling to the Peccei-Quinn breaking vacuum. In this case, the associated gravitational wave signal is more likely to be probed at the proposed Einstein Telescope.

Removing instabilities in the hierarchical equations of motion: Exact and approximate projection approaches.

The hierarchical equations of motion (HEOM) provide a numerically exact approach for computing the reduced dynamics of a quantum system linearly coupled to a bath. We have found that HEOM contains temperature-dependent instabilities that grow exponentially in time. In the case of continuous-bath models, these instabilities may be delayed to later times by increasing the hierarchy dimension; however, for systems coupled to discrete, nondispersive modes, increasing the hierarchy dimension does little to alleviate the problem. We show that these instabilities can also be removed completely at a potentially much lower cost via projection onto the space of stable eigenmodes; furthermore, we find that for discrete-bath models at zero temperature, the remaining projected dynamics computed with few hierarchy levels are essentially identical to the exact dynamics that otherwise might require an intractably large number of hierarchy levels for convergence. Recognizing that computation of the eigenmodes might be prohibitive, e.g., for large or strongly coupled models, we present a Prony filtration algorithm that may be useful as an alternative for accomplishing this projection when diagonalization is too costly. We present results demonstrating the efficacy of HEOM projected via diagonalization and Prony filtration. We also discuss issues associated with the non-normality of HEOM.

A strongly-coupled model for flexible rotors

A fluid–structure model describing the equilibrium state of a flexible blade rotor with its own wake is derived for various external axial flow conditions. The model is based on three building blocks. The two-dimensional lifting-line theory is first used to compute the local aerodynamic loads and the blade circulation profile. The blade deformation is then obtained by solving the nonlinear equations for bending and twisting angles deduced from a one-dimensional beam model. Finally, the wake is obtained using a Joukowski model. In this wake model, the wake of each blade is modeled by two small-core-size counter-rotating vortices emitted from the rotor axis and blade tip. The velocity field induced by these vortices is computed using the Biot–Savart law. We show that, in the rotor frame, we can obtain a stationary vortex structure for almost any vertical flight regimes. This wake solution can then be used to compute the induced velocity in the rotor plane and apply the two-dimensional lifting-line theory again. By iterating a few times this loop, we converge toward a nonlinear solution of the problem for which the aerodynamics loads, blade deformation and wake structure are compatible.As illustration, this newly-developed model is applied to two rotors. We analyze the effects of the external wind conditions, geometry and material properties of the blades on the blade deformation and wake characteristics. We show that we can describe slow descending regimes for which the classical momentum theory does not apply.

How does relativistic kinetic theory remember about initial conditions?

Understanding hydrodynamization in microscopic models of heavy-ion collisions has been an important topic in current research. Many lessons obtained within the strongly-coupled (holographic) models originate from the properties of transient excitations of equilibrium encapsulated by short-lived quasinormal modes of black holes. This paper aims to develop similar intuition for expanding plasma systems described by a simple model from the weakly-coupled domain, the Boltzmann equation in the relaxation time approximation. We show that in this kinetic theory setup there are infinitely many transient modes carrying information about the initial distribution function. They all have the same exponential damping set by the relaxation time but are distinguished by different power-law suppressions and different frequencies of oscillations, logarithmic in proper time. We also analyze the resurgent interplay between the hydrodynamics and transients in this setup.

Heuristic Modeling of Strong Coupling in Plasmonic Resonators

Strong coupling of plasmonic excitations and dipolar emitters, such as organic molecules, have been studied extensively in the last years. The questions whether strong coupling can be achieved with a single molecule only and how this is unambiguously proven are still under debate. A critical issue of plasmonic in contrast to photonic systems is additional excitonic line broadening, which is often neglected when modeling such systems. This has led to too optimistic design predictions or incorrect interpretation of ambiguous experimental data, for example in models relying on Maxwell solvers without self-consistent incorporation of line broadening effects. In this paper, we present a heuristic modeling approach for strongly coupled systems based on plasmonic nanoparticles and dipolar emitters that accounts for such broadening and elucidates on recent experiments with single emitters. We explicitly focus on a clear and intuitive classical description that utilizes well-established methods, easy to use within typical Maxwell solvers. The heuristic model (i) provides experimentally relevant numbers like emitter densities and spectra (ii) allows to discriminate systems, which can reach the strong coupling regime from those, which can not (iii) allows to identify optimization routes and (iv) nicely matches with experimental findings. In particular, we employ an approach related to quasi normal modes and extinction simulations where the excitonic system is represented by a frequency dependent permittivity. As examples, we investigate two configurations with many, but also single emitters, which have been studied in recent experiments.

Z Boson Production in pp Collisions in the Range of the Center-of-Mass Energy from 7 to 100 TeV

High energy physics colliders have been contributing discoveries of and judgments on particles since the early 20th century. One of the well-known high-energy particle colliders is the large hadron collider (LHC), and its proton-proton collision energies have recently been 7, 8 and 13 TeV with the goal of reaching 14 TeV, which is the maximum capacity of the LHC. However, more physics are still to be explored and tested beyond the energy region of the LHC. Therefore, a new collider bigger than the LHC machine, which will be able to collide protons at a 100-TeV center-of-mass energy, is under consideration by the high-energy physics community. To provide insight into the transition from the LHC to the 100-TeV collider, we investigated some properties of the Z process in the collision-energy range from 7 to 100 TeV by using the HERAPDF2.0, MMHT2014, NNPDF3.1 and CT14 next-to-next-to-leading order (NNLO) parton distribution function (PDF) models at NNLO quantum chromodynamics (QCD). The considered properties are the production rate of the Z boson, the change in the uncertainties caused by the collision energy (PDF, renormalization and factorization scales, strong coupling constant, model and parameterization), the forward-backward asymmetry, and the k-factor of the Z boson.

Energy spectrum of graphene with adsorbed potassium atoms

In the present work, we study the influence of adsorbed impurities, namely potassium atoms, on the energy spectrum of electrons in graphene. The electron states of the system are described in the frame of the self-consistent multiband strong-coupling model. It is shown that, at the ordered arrangement of potassium atoms corresponding to a minimum of the free energy, the gap arises in the energy spectrum of graphene. It is established that, at the potassium concentration such that the unit cell includes two carbon atoms and one potassium atom, the latter being placed on the graphene surface above a carbon atom at a distance of 0.286 nm, the energy gap is equal to [Formula: see text]0.25 eV. Such situation is realized if graphene is placed on a potassium support.

Numerical Studies on the Dynamic Responses of Levitated High-temperature Superconductor with a Strongly Coupled Thermo-electromagnetic Model

In this paper, we present a 2-D numerical model based on the H-formulation and nonlinear E-J relationship to study the dynamic responses of a bulk high-temperature superconductor(HTSC) levitated above two kinds of permanent magnetic guideway(PMG). Being different from the existing related models and results of this subject, the thermal effect was brought into account by a strong coupled model with electromagnetic and thermal. The levitation forces were calculated by finite element method and then the vertical motion of the levitated HTSC subject to external disturbance is characterized by a second-order dynamic equation which couples the electromagnetic model via the levitation force. We studied the thermal influence on the vertical force and dynamic characteristics of the HTSC levitated above two kinds of PMGs. The obtained results prove that this strongly coupled model can better simulate the dynamic response of HTSC levitation system.

Electromechanical effects of concentric hypertrophy on the left ventricle: A simulation study

In this work, we analyze the way concentric hypertrophy, triggered by mild aortic stenosis, affects the electromechanical activity of the left ventricle during a cardiac cycle by employing a 3D finite-element strongly-coupled model. Three mechanical feedbacks on electrophysiology are considered: the conduction feedback, acting on conductivity tensors, the convection feedback, dependent on the deformation rate, and the mechanoelectric feedback due to stretch-activated membrane channels. In case of a multiple endocardial electrical stimulation for a healthy ventricle, the convection feedback raises the values of action potential duration APD while modifying the corresponding distribution patterns, mainly in the latest activated regions. Hypertrophy stresses the latter effect. If an endocardial ectopic stimulation is applied to the healthy ventricle, the convection feedback enhances its effects on APD (by increasing the corresponding dispersion too), especially on the opposite side with respect to the stimulation site; the mechanoelectric feedback reduces APD values on the midmyocardium instead. By including all feedbacks, it turns out that the hypertrophic ventricle exhibits lower values and a modified epicardial pattern of APD if compared with the healthy and stenotic (without growth) ventricles, but its transmural dispersion of repolarization does not increase and its epicardial electrograms have the same morphological features. Despite a decrease of the end-diastolic volume, hypertrophy compensates for the stenotic increase of the end-systolic volume and of the internal pressure during the efflux phase, while normalizing stroke work.

Influence of the ordering of impurities on the appearance of an energy gap and on the electrical conductance of graphene

In the one-band model of strong coupling, the influence of substitutional impurity atoms on the energy spectrum and electrical conductance of graphene is studied. It is established that the ordering of substitutional impurity atoms on nodes of the crystal lattice causes the appearance of a gap in the energy spectrum of graphene with width η|δ| centered at the point yδ, where η is the parameter of ordering, δ is the difference of the scattering potentials of impurity atoms and carbon atoms, and y is the impurity concentration. The maximum value of the parameter of ordering is {{boldsymbol{eta }}}_{{boldsymbol{max }}}{boldsymbol{=}}{bf{2}}{boldsymbol{y}}{boldsymbol{,}},{boldsymbol{y}}{boldsymbol{le }}{bf{1}}/{bf{2}}. For the complete ordering of impurity atoms, the energy gap width equals {bf{2}}{boldsymbol{y}}{boldsymbol{|}}{boldsymbol{delta }}{boldsymbol{|}}. If the Fermi level falls in the region of the mentioned gap, then the electrical conductance {{boldsymbol{sigma }}}_{{boldsymbol{alpha }}{boldsymbol{alpha }}}{boldsymbol{to }}{bf{0}} at the ordering of graphene, i.e., the metal–dielectric transition arises. If the Fermi level is located outside the gap, then the electrical conductance increases with the parameter of order η by the relation {{boldsymbol{sigma }}}_{{boldsymbol{alpha }}{boldsymbol{alpha }}}{boldsymbol{ sim }}{{boldsymbol{(}}{{boldsymbol{y}}}^{{bf{2}}}{boldsymbol{-}}frac{{bf{1}}}{{bf{4}}}{{boldsymbol{eta }}}^{{bf{2}}}{boldsymbol{)}}}^{{boldsymbol{-}}{bf{1}}}. At the concentration {boldsymbol{y}}{boldsymbol{=}}{bf{1}}{boldsymbol{/}}{bf{2}}, as the ordering of impurity atoms η →1, the electrical conductance of graphene {{boldsymbol{sigma }}}_{{boldsymbol{alpha }}{boldsymbol{alpha }}}{boldsymbol{to }}{boldsymbol{infty }}, i.e., the transition of graphene in the state of ideal electrical conductance arises.

Strong Coupling of Epsilon-Near-Zero Phonon Polaritons in Polar Dielectric Heterostructures.

We report the first observation of epsilon-near-zero (ENZ) phonon polaritons in an ultrathin AlN film fully hybridized with surface phonon polaritons (SPhP) supported by the adjacent SiC substrate. Employing a strong coupling model for the analysis of the dispersion and electric field distribution in these hybridized modes, we show that they share the most prominent features of the two precursor modes. The novel ENZ-SPhP coupled polaritons with a highly propagative character and deeply subwavelength light confinement can be utilized as building blocks for future infrared and terahertz nanophotonic integration and communication devices.

Theoretical investigation of excitonic magnetism in LaSrCoO4

We use the LDA+U approach to search for possible ordered ground states of LaSrCoO4. We find a staggered arrangement of magnetic multipoles to be stable over a broad range of Co 3d interaction parameters. This ordered state can be described as a spin-density-wave-type condensate of excitons carrying spin S = 1. Further, we construct an effective strong-coupling model, calculate the exciton dispersion and investigate closing of the exciton gap, which marks the exciton condensation instability. Comparing the layered LaSrCoO4 with its pseudo cubic analog LaCoO3, we find that for the same interaction parameters the excitonic gap is smaller (possibly vanishing) in the layered cobaltite.

VPH-HF: A software framework for the execution of complex subject-specific physiology modelling workflows

Computational medicine more and more requires complex orchestrations of multiple modelling & simulation codes, written in different programming languages and with different computational requirements, which when validated need to be run many times on large cohorts of patients. The aim of this paper is to present a new open source software, the VPH Hypermodelling Framework (VPH-HF). The VPH-HF overcomes the limitations of most workflow execution environments by supporting both Taverna and Muscle2; the addition of Muscle2 support makes possible the execution of very complex orchestrations that include strongly-coupled models. The overhead that the VPH-HF imposes in exchange for this is small, and tends to be flat regardless of the complexity and the computational cost of the hypermodel being executed. We recommend the use of the VPH-HF to orchestrate any hypermodel with an execution time of 200 s or higher, which would confine the VPH-HF overhead to less than 10%. The VPH-HF also provide an automatic caching system over the execution of every hypomodel, which may provide considerable speed-up when the orchestration is run repeatedly over large numbers of patients or within stochastic frameworks, and the input sets are properly binned. The caching system also makes it easy to form large input set/output set databases required to develop reduced-order models, and the framework offers the possibility to dynamically replace single models in the orchestration with reduced-order versions built from cached results, an essential feature when the orchestration of multiple models produces a combinatory explosion of the computational cost.

Computational modeling of the electromechanical response of a ventricular fiber affected by eccentric hypertrophy

Abstract The aim of this work is to study the effects of eccentric hypertrophy on the electromechanics of a single myocardial ventricular fiber by means of a one-dimensional finite-element strongly-coupled model. The electrical current ow model is written in the reference configuration and it is characterized by two geometric feedbacks, i.e. the conduction and convection ones, and by the mechanoelectric feedback due to stretchactivated channels. First, the influence of such feedbacks is investigated for both a healthy and a hypertrophic fiber in case of isometric simulations. No relevant discrepancies are found when disregarding one or more feedbacks for both fibers. Then, all feedbacks are taken into account while studying the electromechanical responses of fibers. The results from isometric tests do not point out any notable difference between the healthy and hypertrophic fibers as regards the action potential duration and conduction velocity. The length-tension relationships show increased stretches and reduced peak values for tension instead. The tension-velocity relationships derived from afterloaded isotonic and quick- release tests depict higher values of contraction velocity at smaller afterloads. Moreover, higher maximum shortenings are achieved during the isotonic contraction. In conclusion, our simulation results are innovative in predicting the electromechanical behavior of eccentric hypertrophic fibers.

Excitonic magnetism in d6 perovskites

We use the LDA+U method to study the possibility of exciton condensation in perovskites of transition metals with $d^6$ electronic configuration such as LaCoO$_3$. For realistic interaction parameters we find several distinct solutions exhibiting spin-triplet exciton condensate, which gives rise to a local spin density distribution while the ordered moments are vanishingly small. Rhombohedral distortion from the ideal cubic structure suppresses the ordered state, contrary to the spin-orbit coupling which enhances the excitonic condensation energy. We explain the trends observed in the numerical simulations with the help of a simplified strong-coupling model. Our results indicate that LaCoO$_3$ is close to the excitonic instability and suggest ways to make it order.

The Higgs of the Higgs and the diphoton channel

LHC results do not confirm conventional natural solutions to the Higgs mass hierarchy problem, motivating alternative interpretations where a hierarchically small weak scale is generated from a dimension-less quantum dynamics. We propose weakly and strongly-coupled models where the field that breaks classical scale invariance giving mass to itself and to the Higgs is identified with a possible new resonance within the LHC reach. As an example, we identify such resonance with the 750 GeV diphoton excess recently reported by ATLAS and CMS. Such models can be extrapolated up to the Planck scale, provide Dark Matter candidates and eliminate the SM vacuum instability.

Time-resolved GRB spectra in the complex radiation of synchrotron and Compton processes

Under the steady state condition, the spectrum of electrons is investigated by solving the continuity equation under the complex radiation of both the synchrotron and Compton processes. The resulted GRB spectrum is a broken power law in both the fast and slow cooling phases. On the basis of this electron spectrum, the spectral indices of the Band function in four different phases are presented. In the complex radiation frame, the detail investigation on physical parameters reveals that both the reverse shock photosphere model and the forward shock with strong coupling model can answer the $\alpha \sim -1$ problem. A possible marginal to fast cooling phase transition in GRB 080916C is discussed. The time resolved spectra in different pulses of GRB 100724B, GRB 100826A and GRB 130606B are investigated. We found that the flux is proportional to the peak energy in almost all pulses. The phases for different pulses are determined according to the spectral index revolution. We found the strong correlations between spectral indices and the peak energy in GRB 100826A, which can be explained by the Compton effect in the fast cooling phase. However, the complex scenario predicts a steeper index for the injected electrons, which challenges the acceleration mechanism in GRBs.