Different Degrees Of Coupling Research Articles

General Muscle Torque Generator Model for a Two Degree-of-Freedom Shoulder Joint.

Muscle torque generators (MTGs) have been developed as an alternative to muscle-force models, reducing the muscle-force model complexity to a single torque at the joint. Current MTGs can only be applied to single Degree-of-freedom (DoF) joints, leading to complications in modeling joints with multiple-DoFs such as the shoulder. This study aimed to develop an MTG model that accounts for the coupling between 2-DoF at the shoulder joint: shoulder plane of elevation (horizontal abduction/adduction) and shoulder elevation (flexion/extension). Three different 2-DoF MTG equations were developed to model the coupling between these two movements. Net joint torques at the shoulder were determined for 20 participants (10 females and 10 males) in isometric, isokinetic, and passive tests. Curve and surface polynomial fitting were used to find the best general fit for the experimental data in terms of the different degrees of coupling. The models were validated against experimental isokinetic torque data. It was determined that implicit coupling that used interpolation between single-DoF MTGs resulted in the lowest root-mean-square percent error of 8.5%. The work demonstrated that general MTG models can predict torque results that are dependent on multiple-DoFs of the shoulder.

Mapping orthorhombic domains with geometrical phase analysis in rare-earth nickelate heterostructures

Most perovskite oxides belong to the Pbnm space group, composed of an anisotropic unit cell, A-site antipolar displacements, and oxygen octahedral tilts. Mapping the orientation of the orthorhombic unit cell in epitaxial heterostructures that consist of at least one Pbnm compound is often needed for understanding and controlling the different degrees of coupling established at their coherent interfaces and, therefore, their resulting physical properties. However, retrieving this information from the strain maps generated with high-resolution scanning transmission electron microscopy can be challenging, because the three pseudocubic lattice parameters are very similar in these systems. Here, we present a novel methodology for mapping the crystallographic orientation in Pbnm systems. It makes use of the geometrical phase analysis algorithm, as applied to aberration-corrected scanning transition electron microscopy images, but in an unconventional way. The method is fast and robust, giving real-space maps of the lattice orientations in Pbnm systems, from both cross section and plan-view geometries, and across large fields of view. As an example, we apply our methodology to rare-earth nickelate heterostructures, in order to investigate how the crystallographic orientation of these films depends on various structural constraints that are imposed by the underlying single crystal substrates. We observe that the resulting domain distributions and associated defect landscapes mainly depend on a competition between the epitaxial compressive/tensile and shear strains, together with the matching of atomic displacements at the substrate/film interface. The results point toward strategies for controlling these characteristics by appropriate substrate choice.

Charge carrier dynamics in conducting polymer PEDOT using abinitio molecular dynamics simulations.

As conducting polymers become increasingly important in electronic devices, understanding their charge transport is essential for material and device development. Various semi-empirical approaches have been used to describe temporal charge carrier dynamics in these materials, but there have yet to be any theoretical approaches utilizing abinitio molecular dynamics. In this work, we develop a computational technique based on abinitio Car-Parrinello molecular dynamics to trace charge carrier temporal motion in archetypical conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). Particularly, we analyze charge dynamics in a single PEDOT chain and in two coupled chains with different degrees of coupling and study the effect of temperature. In our model we first initiate a positively charged polaron (compensated by a negative counterion) at one end of the chain, and subsequently displace the counterion to the other end of the chain and trace polaron dynamics in the system by monitoring bond length alternation in the PEDOT backbone and charge density distribution. We find that at low temperature (T = 1K) the polaron distortion gradually disappears from its initial location and reappears near the new position of the counterion. At the room temperature (T = 300K), we find that the distortions induced by polaron, and atomic vibrations are of the same magnitude, which makes tracking the polaron distortion challenging because it is hidden behind the temperature-induced vibrations. The novel approach developed in this work can be used to study polaron mobility along and between the chains, investigate charge transport in highly doped polymers, and explore other flexible polymers, including n-doped ones.

Modifying the trajectory of epicardial leads can substantially reduce MRI-induced RF heating in pediatric patients with a cardiac implantable electronic device at 1.5T.

After epicardial cardiac implantable electronic devices are implanted in pediatric patients, they become ineligible to receive MRI exams due to an elevated risk of RF heating. We investigated whether simple modifications in the trajectories of epicardial leads could substantially and reliably reduce RF heating during MRI at 1.5 T, with benefits extending to abandoned leads. Electromagnetic simulations were performed to assess RF heating of two common 35-cm epicardial lead trajectories exhibiting different degrees of coupling with MRI incident electric fields. Experiments in anthropomorphic phantoms implanted with commercial cardiac implantable electronic devices confirmed the findings. Both electromagnetic simulations and experimental measurements were performed using head-first and feet-first positioning and various landmarks. Transfer function approach was used to assess the performance of suggested modifications in realistic body models. Simulations (head-first, chest landmark) of a 35-cm epicardial lead with a trajectory where the excess length of the lead was looped and placed on the inferior surface of the heart showed an 87-fold reduction in the 0.1 g-averaged specific absorption rate compared with the lead where the excess length was looped on the anterior surface. Repeated experiments with a commercial epicardial device confirmed this. For fully implanted systems following low-specific absorption rate trajectories, there was a 16-fold reduction in the average temperature rise and a 28-fold reduction for abandoned leads. The transfer function method predicted a 7-fold reduction in the RF heating in 336 realistic scenarios. Surgical modification of epicardial lead trajectory can substantially reduce RF heating at 1.5 T, with benefits extending to abandoned leads.

Theory and phenomenology of stressed wave-dark-matter soliton

Soliton in the hostile turbulent wave dark matter ($\mathrm{\ensuremath{\Psi}}\mathrm{DM}$) halo of a galaxy agitates with various kinds of excitation, and the soliton even breathes heavily under great stress. A theory of collective excitation for a $\mathrm{\ensuremath{\Psi}}\mathrm{DM}$ soliton is presented. The collective excitation has different degrees of coupling to negative energy modes, where lower-order excitation generally necessitates more negative energy coupling. A constrained variational principle is developed to assess the frequencies and mode structures of small-amplitude perturbations. The predicted frequencies are in good agreement with those found in simulations. Soliton breathing at amplitudes on the verge of breakup is also a highlight of this work. Even in this extreme nonlinear regime, the wave function perturbation amplitudes are moderate. The simulation data show a stable oscillation with frequency weakly dependent on the oscillation amplitude and hint at a self-consistent quasilinear model for the wave function that accounts for modifications in the ground-state wave function and the equilibrium density. The mock solution, constructed from the simulation data, can shed light on the dynamics of the large-amplitude breathing soliton and support the quasilinear model, as evidenced by its ability to predict well the nonlinear eigenfrequency shifts and large-amplitude breathing frequency observed in simulations.

The Unlocking Process Leading to the 2016 Central Italy Seismic Sequence

AbstractApproximately 23,000 well‐located earthquakes from 2009 to 2016 are used as templates to recover seismic activity preceding the 2016 Central Italy seismic sequence. The resulting spatiotemporal pattern is analyzed by additional ∼91,000 newly detected events. In the 8 years before the sequence onset, seismicity (ML ≤ 3.7) develops at the hangingwall of the 2016 normal faults and along a sub‐horizontal shear zone, bounding the active extensional system at depth. This activity, mainly organized in foreshock‐mainshock and swarm‐like clusters, migrates toward the nucleation area of the first Mw 6.0 mainshock of the sequence (24th of August in Amatrice). We propose an unlocking process based on variable temporal clustering of the seismicity, including repeaters, identifying fault portions with different degrees of coupling. Such a progressive localization of the seismic activity at the fault edges induces a weakening of the locked patch of the Amatrice mainshock.

Seismic Performance of Coupled Steel Plate Shear Walls with Different Degrees of Coupling

Seismic Performance of Coupled Steel Plate Shear Walls with Different Degrees of Coupling

Numerical study of reinforced concrete coupled shear walls based on a two-dimensional finite element model

The reinforced concrete (RC) coupled shear wall is used extensively in high-rise buildings due to its extraordinary lateral resistance performance. Although massive individual RC shear wall as well as RC coupling beam specimens were tested, both the experimental and numerical studies on the seismic performance of RC coupled shear walls are insufficient. Considering the difficulties in large-scale coupled shear wall tests, finite element analysis (FEA) is carried out in this study to reveal quantitatively the effects of coupling beams with different aspect ratios and reinforcement layouts, as well as the behavior of coupling beams in the complex boundary conditions between adjacent wall piers. First, the finite element model based on a two-dimensional fixed crack constitutive model is proposed and validated by twelve coupling beam tests and the results demonstrate that buckling of diagonal bars should be reasonably considered. Then three coupled shear wall specimens are simulated, verifying the high accuracy of the proposed model. The effects of slabs on the coupled shear wall as well as coupling beams are also discussed. Finally, twenty coupled shear wall models with different degrees of coupling (DOCs) and diagonal bar ratios of coupling beams are analyzed. The results demonstrate that coupled shear walls with the diagonal bar ratio of 25–75% exhibit equivalent seismic performance with the diagonal bar ratio of 100%. In order to make full use of the energy dissipation of coupling beams, the DOC value should be no larger than 66%. With the constraint of adjacent wall piers, large axial compressive and tensile forces are induced, and their effects on the coupling beams should be considered.

Efficient dust ring formation in misaligned circumbinary discs

ABSTRACT Binary systems exert a gravitational torque on misaligned discs orbiting them, causing differential precession which may produce disc warping and tearing. While this is well understood for gas-only discs, misaligned cirumbinary discs of gas and dust have not been thoroughly investigated. We perform SPH simulations of misaligned gas and dust discs around binaries to investigate the different evolution of these two components. We choose two different disc aspect ratios: A thin case for which the gas disc always breaks, and a thick one where a smooth warp develops throughout the disc. For each case, we run simulations of five different dust species with different degrees of coupling with the gas component, varying in Stokes number from 0.002 (strongly coupled dust) to 1000 (effectively decoupled dust). We report two new phenomena: First, large dust grains in thick discs pile up at the warp location, forming narrow dust rings, due to a difference in precession between the gas and dust components. These pile ups do not form at gas pressure maxima, and hence are different from conventional dust traps. This effect is most evident for St ∼ 10–100. Secondly, thin discs tear and break only in the gas, while dust particles with St ≥ 10 form a dense dust trap due to the steep pressure gradient caused by the break in the gas. We find that dust with St ≤ 0.02 closely follow the gas particles, for both thin and thick discs, with radial drift becoming noticeable only for the largest grains in this range.

Analytical model for seismic simulation of reinforced concrete coupled shear walls

Reinforced concrete coupled walls are widely used as the main seismic resistant structural system in high-rise buildings. This paper proposes a new mixed beam-shell model for the seismic analysis of reinforced concrete coupled walls with sufficient efficiency and accuracy on the platform of general finite element software MSC.Marc. Boundary elements at the ends of wall piers are simulated by conventional fiber beam-column elements, while the web of the wall pier is modeled by the layered shell element. Coupling beams are simulated by non-conventional fiber beam-column elements, which can not only take into account the shear and shear-sliding deformation together with various failure modes of conventionally reinforced beams, but also the shear and rebar slip deformation of diagonally reinforced beams. RBE2 link elements are utilized to connect the coupling beams to the wall piers. Eight test specimens reported in the literature are used to validate the proposed model. The mechanism of the coupled wall is thoroughly investigated in terms of the beam deformation, base shear and moment distribution as well as axial force of the wall piers. Furthermore, parametric analyses on specimens with different degrees of coupling and types of reinforcement layouts of coupling beams are conducted. Based on the analyses, the influences of the complex behavior and various modeling parameters of coupling beams on the behavior of coupled wall are revealed quantitatively. As a conclusion of the parametric analyses results, it is recommended that the complicated behavior of coupling beams be accurately considered for most cases in the seismic analysis of coupled wall systems.

Lithospheric folding by flexural slip in subduction zones as source for reverse fault intraslab earthquakes

Subduction requires the permanent generation of a bend fold in the subducting slab which mechanics is not well understood. Lithospheric bending of subducting slabs was traditionally considered to be accommodated by orthogonal flexure, generating extensional outer rise earthquakes responsible of the external arc elongation during folding. Here we explore the possibility of lithospheric flexure being accommodated through simple shear deformation parallel to the slab (folding by flexural slip) and evaluate this process as source of earthquakes. The seismicity predicted by flexural slip dominated slab bending explains a significant amount of intermediate earthquakes observed in subduction zones with different degrees of coupling. This mechanism predicts the generation of intraslab thrust earthquakes with fault planes subparallel to the slab top. Being the orientations of the fault planes the same for the interface thrust earthquakes and the flexural-slip intraslab earthquakes, the amount of seismic moment liberated by the interface could be significantly lower than considered before. This proposed seismic source should be taken into account in models and hazard studies of subduction zones. Determining the seismic generating processes in subduction zones and their characteristics is a fundamental issue for the correct assessment of the associated seismic and tsunami risk.

Neogene-quaternary evolution from transpressional to transtensional tectonics in Northern Central America controlled by cocos: Caribbean subduction coupling change

The structural evolution of the western boundary of the Chortis Block, particularly in the Central America Volcanic Arc crossing El Salvador is poorly known. We have done a kinematic analysis from seismic and fault slip data and combined our results with a review of previous regional studies. This approach allowed us to constrain the tectonic evolution and the processes that control the deformation in northern Central America. Along the active volcanic arc we identified active transtensional deformation. On the other hand, we have identified two deformation phases in the back arc region: A first one of transpressional wrenching close to simple shearing (Miocene); and a second one characterized by almost E–W extension coincident with the extensional direction of the Honduras grabens opening. Our results reveal a change from transpressional to transtensional shearing coeval with a migration of the volcanism towards the trench in Late Miocene times. The strain change could be related to a transition from coupled to decoupled interface on the Cocos—Caribbean subduction, which could be caused by a slab roll-back of the Cocos Plate beneath the Chortis Block. The combination of different degrees of coupling on the subduction interface, together with a constant relative eastward drift of the Caribbean Plate, control the deformation style along the western boundary of the Chortis Block.

Aspect ratio effects on revolving wings with Rossby number consideration

Numerical simulations have been conducted to investigate the effect of aspect ratio (AR) on the mean lift generation of a revolving flat rectangular wing. The purpose of the study is to address some discrepancies reported in the literature regarding the influence of AR on mean lift coefficient. Here, we consider a range of AR from 1 to 10 and Rossby number (Ro) from 0.58 to 7.57, and our results show that different degrees of coupling between AR and Ro yield different trends of a mean lift coefficient with respect to increasing AR. The choice of reference velocity for the normalisation of mean lift forces also has a significant effect on the perceived AR effect. By isolating the effect of Ro, we found that higher AR produces higher mean lift coefficient until it plateaus at a sufficiently high AR. This finding is consistent with conventional fixed wing aerodynamics. Additionally, our results show that increasing AR reduces the three-dimensional wing tip effect and is beneficial to mean lift generation while higher Ro increases leading-edge vortex instability, which is detrimental to mean lift generation. Therefore, mean lift generation on revolving wings is dictated by the competition between these two factors, which represent two fundamentally independent phenomena.

On the non-uniqueness of the hydro-geomorphic responses in a zero-order catchment with respect to soil moisture

This study advances mechanistic interpretation of predictability challenges in hydro-geomorphology related to the role of soil moisture spatial variability. Using model formulations describing the physics of overland flow, variably saturated subsurface flow, and erosion and sediment transport, this study explores (1) why a basin with the same mean soil moisture can exhibit distinctly different spatial moisture distributions, (2) whether these varying distributions lead to non-unique hydro-geomorphic responses, and (3) what controls non-uniqueness in relation to the response type. Two sets of numerical experiments are carried out with two physically-based models, HYDRUS and tRIBS+VEGGIE+FEaST, and their outputs are analyzed with respect to pre-storm moisture state. The results demonstrate that distinct spatial moisture distributions for the same mean wetness arise because near-surface soil moisture dynamics exhibit different degrees of coupling with deeper-soil moisture and the process of subsurface drainage. The consequences of such variations are different depending on the type of hydrological response. Specifically, if the predominant runoff response is of infiltration excess type, the degree of non-uniqueness is related to the spatial distribution of near-surface moisture. If runoff is governed by subsurface stormflow, the extent of deep moisture contributing area and its “readiness to drain” determine the response characteristics. Because the processes of erosion and sediment transport superimpose additional controls over factors governing runoff generation and overland flow, non-uniqueness of the geomorphic response can be highly dampened or enhanced. The explanation is sediment composed by multi-size particles can alternate states of mobilization or surface shielding and the transient behavior is inherently intertwined with the availability of mobile particles. We conclude that complex nonlinear dynamics of hydro-geomorphic processes are inherent expressions of physical interactions. As complete knowledge of watershed properties, states, or forcings will always present the ultimate, if ever resolvable, challenge, deterministic predictability will remain handicapped. Coupling of uncertainty quantification methods and space-time physics-based approaches will need to evolve to facilitate mechanistic interpretations and informed practical applications.

On the influence of gravitational and centrifugal buoyancy on laminar flow and heat transfer in curved pipes and coils

The effects of gravitational and centrifugal buoyancy on laminar flow and heat transfer in curved and helical pipes were investigated by numerical simulation. Six dimensionless numbers characterizing the problem were identified, and an analysis was conducted on the possible combinations of signs of the gravitational and centrifugal buoyancy effects. Two distinct Richardson numbers were introduced in order to quantify the importance of the two types of buoyancy, and it was shown that, in the case of heating from the wall, a maximum realizable value of the centrifugal Richardson number exists which is a linear function of the curvature δ (ratio of pipe radius a to curvature radius c). Detailed results were obtained for δ=0.9, torsion λ (ratio of reduced pitch H/(2π) to curvature radius c)=0 (toroidal pipe) or 0.4 (helical pipe), Re=100, Pr=1 and gravitational and centrifugal Richardson numbers Rig, Ric each varying from −0.1 to +0.1. A complex interaction between the two forms of buoyancy was found to exist. In the helical geometry, provided |Rig|≈|Ric| they exhibited effects of the same order. The lowest values of both the friction coefficient and the mean Nusselt number were obtained in the presence of positive gravitational and centrifugal buoyancy, while the highest values were obtained when both forms of buoyancy were negative; the reason for this behavior was identified in the different degree of coupling between the distributions of axial velocity and temperature. In the toroidal geometry, a simpler behavior was predicted due to the presence of top–bottom symmetry; both the friction coefficient and the mean Nusselt number were found to decrease with the intensity of centrifugal buoyancy and to be little affected by gravitational buoyancy in the range of Rig investigated.

Multiscale Modeling of Residual Stress Development in Continuous Fiber-Reinforced Unidirectional Thick Thermoset Composites

The primary objective of this research is to develop a multiscale simulation framework to arrive at more realistic estimates of cure-induced residual stresses in the vicinity of the fiber-matrix interface in thick thermoset composites. The methodology involves simulations at the part level—employing homogenized rendering of the composite using micromechanics approach—within a finite element framework to obtain part-level temperature and degree-of-cure gradients and strains, and imposition of this information as boundary conditions at the mesoscale simulations, employing microstructural representative volume elements (RVE). A simple implementation of the multiscale framework, involving simulations at the part as well as the RVE levels, is demonstrated in the context of a thick, unidirectional continuous-glass-fiber-reinforced thermoset composite. The trends in the mesoscale residual stresses estimated by employing different RVE-level thermal and thermomechanical boundary conditions—displaying different degrees of coupling between the global and part-level simulations—are then examined. Significant differences are observed in the estimates of mesolevel cure-induced residual stress evolution obtained from simulations with a conventional symmetric RVE and those obtained by employing the multiscale approach involving detailed boundary conditions that realistically account for global thermal and mechanical strain histories.

The South Pacific Meridional Mode: A Mechanism for ENSO-like Variability

Abstract In this study, the authors investigate the connection between the South Pacific atmospheric variability and the tropical Pacific climate in models of different degrees of coupling between the atmosphere and ocean. A robust mode of variability, defined as the South Pacific meridional mode (SPMM), is identified in a multimodel ensemble of climate model experiments where the atmosphere is only thermodynamically coupled to a slab ocean mixed layer. The physical interpretation of the SPMM is nearly identical to the North Pacific meridional mode (NPMM) with the off-equatorial southeast trade wind variability altering the latent heat flux and sea surface temperature (SST) and initiating a wind–evaporation–SST feedback that propagates signals into the tropics. The authors also show that a positive cloud feedback plays a role in the development of this mode, but this effect is model dependent. While physically analogous to the NPMM, the SPMM has a stronger expression in the equatorial Pacific and directly perturbs the zonal gradients of SST and sea level pressure (SLP) on the equator, thus leading to ENSO-like variability despite the lack of ocean–atmosphere dynamical coupling. Further analysis suggests that the SPMM is also active in fully coupled climate models and observations. This study highlights the important role of the Southern Hemisphere in tropical climate variability and suggests that including observations from the data-poor South Pacific could improve the ENSO predictability.

Energy-transfer from ultra-small Au nanoclusters to Er³⁺ ions: a short-range mechanism.

Sub-nanometric Au nanoclusters are known to act as very efficient sensitizers for the luminescent emission of Er(3+) ions in silica through a non-resonant broad-band energy-transfer mechanism. In the present work the energy-transfer process is investigated in detail by room temperature photoluminescence characterization of Er and Au co-implanted silica systems in which a different degree of coupling between Er(3+) ions and Au nanoclusters is obtained. The results allow us to definitely demonstrate the short-range nature of the interaction in agreement with non-radiative energy-transfer mechanisms. Moreover, an upper limit to the interaction length is also set by the Au-Au intercluster semi-distance which is smaller than 2.4 nm in the present case.

Quantifying different degrees of coupling in detrended cross-correlation analysis

Detrended cross-correlation analysis provides a scaling exponent that should characterize the power-law cross-correlation of two simultaneously recorded series. This exponent by itself is not able to guarantee the presence of cross-correlation, being strongly influenced by the auto-correlation properties of the single series. Through the use of σDCCA coefficients and simulation with ARFIMA models we built families of curves that can be used as templates to correctly detect the power-law behaviour and quantify the degree of coupling between series with any degree of auto-correlation.

Nano and picosecond magnetization dynamics of weakly coupled CoFe/Cr/NiFe trilayers studied by a multitechnique approach

We present results on the magnetization dynamics in heterostructures of the CoFe/Cr/NiFe type. We have employed a combination of different layer-selective methods covering a broad range from quasistatic hysteresis measurements by x-ray magnetic circular dichroism (XMCD), over time-resolved photoemission electron microscopy (PEEM) at subnanosecond timescales to high-frequency ferromagnetic resonance (FMR) experiments. With increasing driving frequency, we found a different influence of the coupling between the two ferromagnetic layers on the dynamic behavior. Employing the spatial resolution of the PEEM method, we have been able to discern various dynamic responses in different regions of the sample that could be attributed to magnetodynamic processes with a different degree of coupling. In conjunction with the complementary FMR and XMCD measurements, we attribute the inhomogeneous influence of interlayer coupling to a shift from domain-wall-motion-dominated dynamics at low frequencies to precession-dominated dynamics at higher frequencies.