Nonuniform State Research Articles

The energy dispersion of magnetic Rossby waves in zonally nonuniform basic states

The energy dispersion of magnetic Rossby waves was investigated by applying two-dimensional incompressible magnetohydrodynamic equations in both zonally varying basic flow and basic magnetic field. A derived cubic dispersion relation suggests that there are at most three types of magnetic Rossby wave. Two of them represent waves that gradually tend to Alfvén waves during the energy dispersion process. The energy dispersion trajectories (wave rays) finally move with the zonal group velocity that tends to be equal to the zonal phase speed after being reflected by at least one turning location at which the meridional group velocity equal to zero. Along the marching rays, both the wave action density and wave energy tend to be constant values while the wave amplitude will decrease with increasing total wavenumber. The third one represents a wave that gradually have the constant meridional wavenumber, wave action density, wave energy, and wave amplitude. However, the difference in the zonal group velocity and the zonal phase speed suggests that the wave is still dispersive. This type of wave will disappear if specifying uniform basic magnetic field. The cubic dispersion relation is then reduced to a quadratic one. Correspondingly, the remaining two dispersion relations feature a fast- and a slow-propagating magnetic Rossby wave, respectively. They finally tend to be Alfvén waves with no energy dispersion when the energy dispersion process completes.

Estimation of tension distribution on drumheads by visualization of high-order modes using Fourier transform profilometry

In this study, higher vibration modes of drumheads were visualized using Fourier transform profilometry (FTP) for simplifying drum tuning process. In our previous work, we confirmed that images of the (1,1) mode of a drumhead had some curved nodal lines due to non-uniform tension and that it provided visual cues on the state of drum tuning. However, when there were two areas with low tension on a drumhead, non-uniform tension did not curve the nodal lines. Therefore, focusing only on the (1,1) mode can lead to misinterpreting a non-uniform state as uniform. In this research, we expand the scope of visualization to higher modes in order to alleviate this problem. If nodal lines can be visualized even in higher modes, information not included in the (1,1) mode can be obtained, which will allow us to know the tuning state more faithfully. In a visualization experiment, we focused mainly on the (2,1) mode, which consists of two nodal lines. FTP-based visualization confirmed that even when the tension distribution had two areas with low tension, those nodal lines curved around each area. Based on this, it became able to estimate tension distribution that had been challenging with only the (1,1) mode considered.

Rich methane oxidation on Pt/Pd/Al2O3: Steady state performance, multiplicity features, and spatial patterns

Performance features are reported for the catalytic sub-stoichiometric (rich) oxidation of methane on a Pt + Pd/Al2O3 washcoated monolith over a range of feed temperatures and O2/CH4 for both dry and wet feeds. Near isothermal steady state multiplicity and co-existing states with different methane conversions are presented. The methane conversion vs. O2 feed concentration consists of a higher conversion regime at lower concentrations and a lower conversion, inhibited regime at higher concentration. The conversion maximum is accompanied by an overlap of the two regimes in the form of a clockwise hysteresis loop. Spatial concentration profiles for the dry feed reveal an upstream oxidation zone and downstream stream reforming zone. Measurements extending beyond the catalyst imply the co-existence of active and inhibited states. Addition of water promotes oxidation and steam reforming while the multiplicity and nonuniform states persist. Underlying mechanistic aspects responsible for the inhibition, rate multiplicity and co-existing states are discussed.

Simulation study of a semi-circular Caisson Breakwater in a Non-uniform State in a Shallow Water Situation

Simulation study of a semi-circular Caisson Breakwater in a Non-uniform State in a Shallow Water Situation

A Self-Adaptive Double Q-Backstepping Trajectory Tracking Control Approach Based on Reinforcement Learning for Mobile Robots

When a mobile robot inspects tasks with complex requirements indoors, the traditional backstepping method cannot guarantee the accuracy of the trajectory, leading to problems such as the instrument not being inside the image and focus failure when the robot grabs the image with high zoom. In order to solve this problem, this paper proposes an adaptive backstepping method based on double Q-learning for tracking and controlling the trajectory of mobile robots. We design the incremental model-free algorithm of Double-Q learning, which can quickly learn to rectify the trajectory tracking controller gain online. For the controller gain rectification problem in non-uniform state space exploration, we propose an incremental active learning exploration algorithm that incorporates memory playback as well as experience playback mechanisms to achieve online fast learning and controller gain rectification for agents. To verify the feasibility of the algorithm, we perform algorithm verification on different types of trajectories in Gazebo and physical platforms. The results show that the adaptive trajectory tracking control algorithm can be used to rectify the mobile robot trajectory tracking controller’s gain. Compared with the Backstepping-Fractional-Older PID controller and Fuzzy-Backstepping controller, Double Q-backstepping has better robustness, generalization, real-time, and stronger anti-disturbance capability.

Modeling local thermal responses of individuals: Validation of advanced human thermo-physiology models

Human thermo-physiology models (HTPM) are useful tools to assess dynamic and non-uniform human thermal states. However, they are developed based on the physiological data of an average person. In this paper, we present a detailed evaluation of two sophisticated and well-known models, JOS3 and ThermoSEM, with the objective to evaluate their capabilities in predicting the local skin temperature of individual people as both models use individual parameters such as sex, height, weight, and fat percentage as input. For the purpose of validation, controlled experiments were conducted with six human subjects (3 males, 3 females) at different environmental conditions (22–28 °C). The measured core temperature and the local skin temperature at 14 locations were used to evaluate the predicted values. Outputs from both HTPMs followed the dynamic trend of the experiments, with a root mean squared error (RMSE) of 0.9–0.3 °C for core temperature and 1.3–0.9 °C for mean skin temperature from both ThermoSEM and JOS3 correspondingly. However, the main errors came from the body extremities. The RMSE was different for each subject, and both models showed lower errors in the warmer environment. The average RMSE for the hands of all subjects was 2 °C from ThermoSEM and 1.9 °C from JOS3, while it was 0.8 °C for the forehead in both models. The paper highlights the capabilities and limitations of the selected HTPMs and, furthermore, discusses the application of HTPMs in the field of personalized thermal comfort.

Influence of the Straining Path during Cold Drawing on the Hydrogen Embrittlement of Prestressing Steel Wires

Cold drawing is a commonly used technique for manufacturing the prestressing steel wires used as structural elements in prestressed concrete structures. As a result of this manufacturing process, a non-uniform plastic strain and residual stress states are generated in the wire. These stress and strain fields play a relevant role as the main cause of the in-service failure of prestressing steel wires in the presence of an aggressive environment, hydrogen embrittlement (HE). In this paper, hydrogen susceptibility to HE is compared in two different commercial cold-drawn wires with the same dimensions at the beginning and at the end of manufacturing that follow different straining paths. To achieve this goal, numerical simulation with the finite element (FE) method is carried out for two different industrial cold-drawing chains. Later, the HE susceptibility of both prestressing steel wires was estimated in terms of the hydrogen accumulation given by FE numerical simulations of hydrogen diffusion assisted by stress and strain states, considering the previously obtained residual stress and plastic strain fields generated after each wire-drawing process. According to the obtained results, the hardening history modifies the residual stress and strain states in the wires, affecting their behavior in hydrogen environments.

Effect of backfilled stone/brine media on the long‐term free corrosion and electrochemical performance of an aluminum sacrificial anode

AbstractAn Al–Zn–In–Si–Sn–Ti sacrificial anode, utilized to protect steel shells of subsea‐immersed tunnels, works in a backfilled stone (6–10 mm)/brine (40 Ω cm) media (125 Ω cm). This paper investigated its impact on the anode's long‐term free corrosion and electrochemical performance. After prolonged free corrosion, the anode's general corrosion rate is minimal. Although its capacity (Q) and current efficiency (η) increase slightly, it shows a nonuniform dissolution state. Over a long‐term working period, a significant amount of Al(OH)3 deposits and diffuses between the backfilled stone toward the cathode surface, creating distinct stone impressions and a thick product layer. These effects considerably increase the media ρ around the anode and continuously decrease the brine's pH, decreasing Q and η values and output currents. Nonetheless, the current distribution within the media gradually becomes uniform with time, resulting in a homogeneous potential distribution along the cathode.

Stimuli-Responsive Langmuir Films Composed of Nanoparticles Decorated with Poly(N-isopropyl acrylamide) (PNIPAM) at the Air/Water Interface.

The nanotechnology shift from static toward stimuli-responsive systems is gaining momentum. We study adaptive and responsive Langmuir films at the air/water interface to facilitate the creation of two-dimensional (2D) complex systems. We verify the possibility of controlling the assembly of relatively large entities, i.e., nanoparticles with diameter around 90 nm, by inducing conformational changes within an about 5 nm poly(N-isopropyl acrylamide) (PNIPAM) capping layer. The system performs reversible switching between uniform and nonuniform states. The densely packed and uniform state is observed at a higher temperature, i.e., opposite to most phase transitions, where more ordered phases appear at lower temperatures. The induced nanoparticles' conformational changes result in different properties of the interfacial monolayer, including various types of aggregation. The analysis of surface pressure at different temperatures and upon temperature changes, surface potential measurements, surface rheology experiments, Brewster angle microscopy (BAM), and scanning electron microscopy (SEM) observations are accompanied by calculations to discuss the principles of the nanoparticles' self-assembly. Those findings provide guidelines for designing other adaptive 2D systems, such as programable membranes or optical interfacial devices.

Generation of non-uniformly correlated sources with controllable beam profile by devising its statistics in the spatial frequency domain.

We introduce an efficient approach to simultaneously tailor the spatial profile and the degree of coherence (DOC) of partially coherent light by devising its statistical properties in the spatial frequency domain. The relationship between the beam profile and the DOC in the source plane and the correlation function and power spectrum in the spatial frequency domain is analyzed in detail. This approach enables us to generate partially coherent sources with spatially uniform or non-uniform coherence states, and the source profiles are controlled. The condition for switching two coherence states is given through two theoretical examples. Furthermore, we validate our approach in experiment through generating two kinds of spatially non-uniform correlated sources with controllable beam profiles. The experimental results agree well with our theoretical analysis.

Thermal runaway propagation characteristics of lithium-ion batteries with a non-uniform state of charge distribution

Thermal runaway propagation characteristics of lithium-ion batteries with a non-uniform state of charge distribution

Multiple scours and upward fining caused by hydraulic jumps: implications for the recognition of cyclic steps in the deepwater stratigraphic record

ABSTRACT Hydraulic jumps control the bypass, erosion, and depositional processes of Froude-supercritical turbidity currents, so they represent a significant process for understanding the development of submarine geomorphology. Hydraulic jumps actively occur from submarine canyons to fans, where the seafloor slope is relatively steep. Turbidites in such areas comprise large-scale bedforms called cyclic steps, and they exhibit complex internal structures, including localized erosion and the accumulation of coarse-grained fining-upward sequences. However, it is unclear which turbidity-current properties are reflected in the heterogeneous depositional characteristics and grain-size sorting of these deposits. To this end, we conducted flume experiments to reproduce deposits associated with the hydraulic jumps of surge-type flows. Turbidity-current surges were repeatedly generated in an experimental flume with a knickpoint that transitioned from a steep to a gentle slope, resulting in cyclic steps. Overall, the upstream migration of the cyclic steps produced a downstream-upward-fining succession of turbidites. However, hydraulic jumps occurred at several places over the trough to the stoss side of the step in a single flow due to the non-uniform and unsteady flow state of the surge-type turbidite succession. As a result, the reproduced succession exhibited multiple local scours and coarse-grained fill in the lower parts of the turbidites. This suggests that multiple local scours and fining-upward trends are discriminant characteristics of cyclic-step deposits formed by surge-type supercritical turbidity currents.

Switching Impulse Flashover Performance of Nonuniform Pollution Insulators in Natural Environment

Under natural conditions, insulators show a nonuniform pollution state, which has a great influence on the switching impulse flashover voltage of insulators. Meanwhile, the insulation level of transmission lines is selected according to the switching impulse flashover voltage of nonuniform pollution insulators. For this purpose, in this article, the wet pollution method is used to simulate nonuniform pollution conditions. Then, the switching impulse flashover tests and the switching impulse flashover tests with preloading ac voltage are conducted on two types of insulators, XP-70 and LXY-70, in natural environment. The flashover voltage of insulators is obtained, flashover performances are analyzed, and the flashover processes of insulators are photographed. Moreover, the equations of flashover voltage gradient <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{{50}}$ </tex-math></inline-formula> under nonuniform pollution conditions are established. The results indicate that there is a conspicuous polarity effect and a polarity reversal phenomenon under different conditions. Besides, as the increase of the ratio of bottom surface pollution to top surface pollution, the flashover voltage changes in the opposite case of preloading and non-preloading ac voltage. Finally, the switching impulse flashover voltage of ordinary porcelain and glass suspension insulators under nonuniform pollution conditions can be calculated based on the established equations of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{{50}}$ </tex-math></inline-formula> . The results can provide theoretical support for the reasonable selection of the insulation level of transmission lines, which in turn can greatly reduce the cost of the transmission lines.

Longitudinal evolution from scalar to vector beams assembled from all-dielectric metasurfaces.

Vector vortex beams (VVBs) with non-uniform polarization states have a wide range of applications, from particle capture to quantum information. Here, we theoretically demonstrate a generic design for all-dielectric metasurfaces operating in the terahertz (THz) band, characterized as a longitudinal evolution from scalar vortices carrying homogeneous polarization states to inhomogeneous vector vortices with polarization singularities. The order of the converted VVBs can be arbitrarily tailored by manipulating the topological charge embedded in two orthogonal circular polarization channels. The introduction of the extended focal length and the initial phase difference effectively guarantees the smoothness of the longitudinal switchable behavior. A generic design approach based on vector-generated metasurfaces can assist in the exploration of new singular properties of THz optical fields.

Finite-Element Modeling of FRP-Confined Noncircular Concrete Columns Using the Evolutionary Potential-Surface Trace Plasticity Constitutive Model for Concrete

The compressive behavior of fiber-reinforced polymer (FRP)-confined concrete columns with a noncircular cross section has been investigated through extensive experimental, analytical, and numerical research, but a unified theoretical/numerical approach that can accurately predict both their section-average behavior and local concrete behavior is not yet available. In noncircular columns under axial compression, the concrete is typically under a nonuniform stress state of three-dimensional (3D) compression, with the lateral compressive stresses being the reactive stresses from the confining device (i.e., passive confinement). The authors of the present paper recently developed a plasticity constitutive model for concrete under general 3D compressive stresses, which possesses a potential surface with an evolutionary deviatoric trace that can accurately capture the results of existing compression tests of concrete cubes under nonuniform, passive confinement. This paper explores the application and capability of this evolutionary potential-surface trace (EPT) plasticity constitutive model in finite-element (FE) analysis of FRP-confined square, rectangular, and elliptical plain-concrete columns under concentric compression. The section-average behavior of all the selected noncircular columns predicted by these FE analyses was close to the existing experimental data. The numerical results obtained with the EPT plasticity constitutive model were then examined in detail to achieve an improved understanding of local concrete behavior in FRP-confined noncircular columns.

Improved mechanical properties of Co-free high-entropy Cantor alloy: A first-principles study

High-entropy alloys (HEAs) have received attention because of their excellent mechanical and thermodynamic properties. A recent study revealed that Co-free face-centered cubic HEAs could improve strength and ductility, which is crucial for nuclear materials. Here we implemented first-principles calculations to explore the fundamental mechanism for enhancing the mechanical properties in Co-free Cr25Fe25Ni25Mn25 alloy. We found that the local lattice distortion of Co-free HEA was more significant than that of the well-known Cantor alloy. Furthermore, the short-range order formation in Co-free HEA caused the highly fluctuated stacking fault energy. Thus, the significant local lattice distortion and the non-uniform solid solution states comprising low- and high-stacking fault regions improve strength and ductility.

On a hypercycle equation with infinitely many members

A hypercycle equation with infinitely many types of macromolecules is formulated and studied both analytically and numerically. The resulting model is given by an integro-differential equation of the mixed type. Sufficient conditions for the existence, uniqueness, and non-negativity of solutions are formulated and proved. Analytical evidence is provided for the existence of non-uniform (with respect to the second variable) steady states. Finally, numerical simulations strongly indicate the existence of a stable nonlinear wave in the form of the wave train.

MODELLING AND ANALYSIS OF INITIAL STRESS STATE IN A THIN-WALL CYLINDER WITH VARIABLE CHARACTERISTICS

A linearized model of prestressed elastic body vibrations is described in terms of the nonsymmetric Piola stress tensor, and a weak statement of the original problem is given. With the help of the Lagrange variational principle, we construct a statement of the problem of steady axisymmetric oscillations of a thin-walled (shell-like) cylinder with variable material properties in the presence of an inhomogeneous prestress field. The motion equations, essential and natural boundary conditions are formulated. Integral characteristics are introduced that average the change in prestresses and material properties over the shell thickness. On the basis of the model presented, the problem on steady-state vibrations of a functionally graded prestressed cylindrical shell is numerically investigated via the shooting method; the influence of the laws of change in material modules and prestress components on dynamic characteristics (e.g., amplitude-frequency characteristics, natural vibration frequencies) is analyzed, a comparative analysis of the solutions is carried out depending on the thin-walled parameter. For the considered cylindrical shell with axial inhomogeneity, based on the acoustic sounding data, we study the inverse problem of restoring two laws of prestress inhomogeneity characterizing the nonuniform initial stress-strain state of tension or inflation. As additional information, we consider the measurement data of the displacement components on the cylinder's surface, given in a set of points at a certain frequency of steady-state oscillations; in such a case, the material characteristics are considered to be known and may depend on the axial coordinate, which makes it possible to set an arbitrary functional gradient along the axis of the cylinder. The mode of probing loading is determined by specifying the traction type and oscillation frequency. Explicit formulas for the desired laws of prestress inhomogeneity are obtained, and computational experiments are carried out to restore them. A high accuracy of reconstruction is revealed far from the ends of the cylinder when probing at a frequency in the vicinity of the first resonance.

Estimating ductile crack initiation in structural steel under combined tension and shear stress using a modified void growth model

Ductile fracture initiation is one of the important issues in recent research on structural steels. Many models have been established to simulate the mechanism of ductile fracture and predict the ductile crack initiation in different loading conditions. The void growth model is one of the most successful micro-models that is originally developed to estimate ductile crack initiation in the first mode of fracture under monotonic loading. However, one of the main shortcomings of these types of uncoupled void growth models is the incapability of them in capturing the behavior of steels under shear stress and the effect of it on the resulting voids and the process of ductile fracture in low and moderate-stress triaxialities. A newly proposed modified void growth model represented in this article is able to overcome this issue by introducing normalized maximum shear stress. A series of scanning electron microscopy examinations and experimental and numerical monotonic tensile examinations have been carried out on the notched round bar and flat groove plate specimens with different notch radii to calibrate the represented fracture model. Steel-holed plates with symmetric notches around the hole and notched shear plates have been tested and analyzed to demonstrate the application and validation of the represented void growth model in predicting the initiation of ductile fracture in various combinations of tension and shear under monotonic loading. Different angles of notches were used in the specimens to achieve diverse stress states to examine the application of the represented micro-model in non-uniform stress state fields. Finally, the role of the characteristic length, as the representative of the density of the inclusions in the material, on the accuracy of the model has been discussed in this article.

An improved stabilized peridynamic correspondence material model for the crack propagation of nearly incompressible hyperelastic materials

An improved stabilized peridynamic correspondence material model (IS-PD-CMM) is proposed in this paper to simulate the crack propagation of nearly incompressible hyperelastic materials. A shape-associated micromodulus as the correction coefficient (penalty factor) is introduced into the modified force state in the IS-PD-CMM to control the deformation caused by nonuniform deformation vector state. Different from the conventional stabilization method, the penalty factor in the IS-PD-CMM is only related to the material properties and does not require the parameter calibration. In addition, an equivalent strain function is introduced into the IS-PD-CMM as the failure criterion for the nearly incompressible hyperelastic material, where the nonlocal damage of the model is determined by calculating the ratio of bond breakages of material particles. The high accuracy and adaptability of the IS-PD-CMM are demonstrated by three representative examples including the infinitesimal deformation of linear elastic materials and the finite deformation of hyperelastic materials. Finally, the in-plane tensile fracture behavior and the out-of-plane tearing fracture behavior are simulated and analyzed to illustrate the good performance of the IS-PD-CMM in predicting the crack propagation of nearly incompressible hyperelastic materials.