Thermally activated delayed fluorescence (TADF) is beneficial for improving the efficiency of organic light‐emitting diodes (OLEDs) by providing pathways to convert non‐emissive triplet excitons into ...singlet excitons. To ensure TADF is efficient, it is critical to enhance the reverse intersystem crossing (RISC) rate. To this end, most approaches propose thus far have focused on reducing the energy difference between S1 and T1 states. The present study explores how incorporating the internal heavy atom (IHA) effect can impact the RISC and device performance. By introducing a series of halogen atoms to charge‐transfer molecules, TADF molecules exhibiting RISC over 7 × 107 s−1 are realized. These molecules are then applied to OLEDs, and the effect of incorporating these moieties is investigated. The results show that efficiency roll‐off is still significant even with RISC‐enhanced TADF emitters. Spectroscopic and theoretical results indicate that a fast RISC may not be the sole factor important for reducing efficiency roll‐off and that the spin‐flip cycles considering both T1→S1 and S1→T1 should be carefully taken into account to derive a complete picture of the IHA effect on efficiency roll‐off behavior.
This study explores how incorporating the internal heavy atom (IHA) effect can impact the reverse intersystem crossing (RISC) and device performance. The spectroscopic and theoretical results indicate that a fast RISC may not be the sole factor important for reducing efficiency roll‐off and that the spin‐flip cycles should be carefully considered to derive a complete picture of the IHA effect.
In this study, Linear Elastic Fracture Mechanics (LEFM) approach is used to evaluate the fatigue strength of a box-shaped welded structure. A parametric study is also undertaken to study the effect ...of various weld parameters on the fatigue strength, such as lack of weld metal penetration, load position, and plate thicknesses. FRANC3D software was adopted to obtain the stress intensity factor values for two types of full-length and intermediate crack sizes, located at the critical region of the weld of the box-shaped structure. It was concluded that the LEFM approach could capture the crack propagation from the weld root reasonably well under the given conditions and estimate residual fatigue life of the welded structures conservatively. Compared to fatigue life estimations by nominal stress method (1,714,564 cycles) or effective notch stress method (63,385 cycles), the LEFM approach can estimate the residual life more accurately. Especially for intermediate (4 mm) lack of penetration (LOP) of weld metal case (589,198 cycles) in comparison to the experiments (1,216,595 cycles). The parametric study showed that the fatigue life increases with increase in the thickness of flanges, lesser LOP in the weld root, and when load is applied more toward the center of the plate.
•Proposed a new ultrasonic assisted single-grain scratching model.•UAS showed higher efficiency while enduring severer wear.•The experimental data coincided well with theoretical calculations ...regarding scratching force and material removal rate.•The factors kL and kH changed from constants to variations due to the ultrasonic effect.
Ultrasonic assisted grinding (UAG) has been demonstrated to be effective for processing hard and brittle materials. In some of the current UAG models, the high efficiency of UAG was attributed to the great maximum momentary force brought by ultrasonic vibration. However, the models were built based on multi-grains behavior which lacks of necessary support by single-grain models and experiments. In this paper, a model for ultrasonic assisted scratching (UAS) was proposed to investigate the cutting behavior of single-grains. The experiments with and without ultrasonic assistance were both conducted on a reaction-bonded silicon carbide specimen to verify the developed model. Results showed that even with the same maximum momentary force, the material removal rate increased greatly with ultrasonic assistance. The factor kL and kH did not remain constants as in the original indentation fracture mechanics models, and were highly related to the amplitude of the ultrasonic vibration.
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We use the particle flow code PFC3D to simulate the triaxial compression of sandstone under various radial stresses and loading strain rates to determine the triaxial stress-strain curves, crack ...propagation path, and contact forces to investigate the failure process of sandstone. We analyze the energy and damage evolution during triaxial compression. The results indicate that the tension and shear-induced cracks increase with the increase of radial stress under the same loading strain rate. Both normal and tangential contact forces exhibit strong anisotropy and increase with radial stress and strain rate. The normal contact force has an approximately symmetrical distribution with respect to the horizontal plane, whereas the tangential contact force has an approximately symmetrical distribution with respect to the axis. For the characteristics of the energy evolution, the boundary energy density, strain energy density, and dissipated energy density all increase linearly with the radial stress, and the boundary energy density increases at the fastest rate, followed by the strain energy density and dissipated energy density. In the post-peak stage the primary energy consumption is the dissipated energy. After that, in the remaining stage the strain energy decreases gradually. By analyzing the evolution of the damage variables in the prepeak area we observed that the damage variable followed an exponential relationship with the axial strain. When the loading strain rate is constant, the damage variable corresponding to the same strain value decreases with increase of radial stress. The results indicate that the increase in radial stress delays the damage acceleration. In contrast, the effect of the loading strain rate on the damage variable is small. The findings reveal the internal structural evolution of rocks during deformation and failure.
The principles of continuum damage mechanics are applied to predict the rolling/sliding contact fatigue crack initiation. The approach involves evaluating the subsurface stresses as well as the state ...of damage within the contact region. It is shown that the fatigue crack initiation life can be related to the scalar damage parameter
D, which is a measure of micro-crack and voids density in the material. Comparison of the predicted results with the available experimental work shows good agreement. The effect of variable loading on the fatigue behavior of rolling contact with provision for non-linear damage evolution is also investigated.
► This paper bridges the continuum damage mechanics and tribology. It is shown that the fatigue crack initiation life for a rolling/sliding element can be related to a scalar damage parameter
D, which is a measure of micro-cracks and voids density in the material. ► The approach utilizes a non-linear thermodynamic-based damage evolution formula in which the damage status at each cycle depends on the loading condition and damage status of the previous cycle. ► It is shown that for rolling/sliding element under cyclic loading condition, the rate of damage evolution increases as time goes on due to the increase in the local stresses. ► On contrary to available contact fatigue models that use linear damage evolution, the results show different damage status inside the material due to different loading sequences. ► It is shown that the existing equations for the prediction of rolling/sliding element life should be modified in a more general form taking loading sequence into consideration.
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•Competitive Adsorption of CO2/CH4 on coal is modeled using statistical mechanics.•The theoretical model provides isotherm and adsorption parameters.•Machine learning is used to ...predict adsorption of CO2/CH4 on various types of coals.•The ML model reliably predicts the competitive adsorption of CO2/CH4 on coals.•Relative importance of features of coals is compared based on the ML approach.
Understanding the adsorption behavior of CO2, CH4, and their mixture on coal at high pressures is necessary to achieve enhanced CH4 recovery and the simultaneous sequestration of CO2. The adsorption of CO2 and CH4 on dry coal is known to exhibit complex behavior as a function of temperature, pressure, and composition. In this study, a model for CO2 adsorption under supercritical conditions was proposed based on a combination of surface adsorption and dissolution in the coal matrix. However, the corresponding CH4 adsorption can only be presented by a surface mechanism. Although the theoretical model provides an idealized description of the heterogeneous nature of coal, it retains the ability to capture the qualitative features of the experimental isotherms. The results indicate reasonable adsorption on the coal surface and dissolution into the coal matrix in the model mechanisms. The model also provides binding energies, surface areas, absolute adsorption isotherms, and isotherms in terms of the fractional occupancy. Considering the complex behavior of mixture adsorption, a machine learning (ML) approach was applied to the adsorption data of various coals. The ML model was reliable for predicting the competitive adsorption of CO2 and CH4 regardless of the coal type (R2 = 0.9950 and 0.9923 for CO2 and CH4, respectively). According to the analytical results obtained from the theoretical model and the ML approach, the volatile matter content, fixed carbon content, and vitrinite reflectance of coal were determined to be important properties for predicting the competitive adsorption of CO2 and CH4 on coal.
How tissue shape emerges from the collective mechanical properties and behavior of individual cells is not understood. We combine experiment and theory to study this problem in the developing wing ...epithelium of Drosophila. At pupal stages, the wing-hinge contraction contributes to anisotropic tissue flows that reshape the wing blade. Here, we quantitatively account for this wing-blade shape change on the basis of cell divisions, cell rearrangements and cell shape changes. We show that cells both generate and respond to epithelial stresses during this process, and that the nature of this interplay specifies the pattern of junctional network remodeling that changes wing shape. We show that patterned constraints exerted on the tissue by the extracellular matrix are key to force the tissue into the right shape. We present a continuum mechanical model that quantitatively describes the relationship between epithelial stresses and cell dynamics, and how their interplay reshapes the wing.
Supported by the wide range of available medical data available, cardiac biomechanical modeling has exhibited significant potential to improve our understanding of heart function and to assisting in ...patient diagnosis and treatment. A critical step towards the development of accurate patient-specific models is the deployment of boundary conditions capable of integrating data into the model to enhance model fidelity. This step is often hindered by sparse or noisy data that, if applied directly, can introduce non-physiological forces and artifacts into the model. To address these issues, in this paper we propose novel boundary conditions which aim to balance the accurate use of data with physiological boundary forces and model outcomes through the use of data-derived boundary energies. The introduced techniques employ Lagrange multipliers, penalty methods and moment-based constraints to achieve robustness to data of varying quality and quantity. The proposed methods are compared with commonly used boundary conditions over an idealized left ventricle as well as over in vivo models, exhibiting significant improvement in model accuracy. The boundary conditions are also employed in in vivo full-cycle models of healthy and diseased hearts, demonstrating the ability of the proposed approaches to reproduce data-derived deformation and physiological boundary forces over a varied range of cardiac function.
•Development of boundary conditions using patient-specific data.•A systematic analysis of cardiac mechanics boundary conditions.•Demonstration of efficacy for 6 patient-specific models.•Novel quantitative comparison with non-invasive imaging data.
Internal Heavy Atom Effect
In article number 2104646, Jihoon Lee, Min Chul Suh, Seunghyup Yoo, and co‐workers show how incorporating the internal heavy atom (IHA) effect can impact the reverse ...intersystem crossing (RISC) and device performance. The spectroscopic and theoretical results indicate that a fast RISC may not be the sole factor important for reducing efficiency roll‐off and that the spin‐flip cycles considering both T1 → S1 and S1 → T1 should be carefully taken into account to derive a complete picture of the IHA effect on efficiency roll‐off behavior.
•Failure process of roof was divided into four stages accompanied with crack propagation.•A fracture mechanics model was established for layered roof crack propagation analysis.•Crack deflection ...mechanism was revealed by considering bedding effect.•Influencing degree of various factors on crack propagation in layered roof was analyzed.
Roof failure significantly threatens the safety and stability of grottoes. For the layered roof of sandstone grottoes, the failure process is closely related to bedding effects of crack propagation. Taking the Yuanjue Cave as an example, the progressive failure process of the layered roof was summarized. The mechanisms of crack propagation in the roof were analyzed theoretically, and bedding effects together with influencing factors of crack propagation were explored. Results showed that the instability process of the layered roof in sandstone grottoes can be summarized into four stages: tensile fracture of the roof, vertical expansion of cracks, horizontal deflection of cracks, and instability collapse of blocks. The development and propagation of cracks constituted the intrinsic cause of the instability of layered roofs. A fracture mechanics model for crack propagation in layered roofs was established considering the bedding effect, and the criteria for vertical expansion of cracks in grotto roofs was derived. Moreover, the fracture criterion of crack competition was modified in combination with the bedding effect, revealing that an increase in interlaminar cohesion inhibited the crack deflection mode. The crack deflection mode in grotto roofs was jointly determined by the stress at the crack-tip (σfxx and σfyy), the strength of the rock layers and bedding plane (σ't, μ and c). To control the crack propagation in roofs, the engineering reinforcement of grotto roofs can be achieved by weakening bedding effects and indirectly reducing the roof span. This study is of great significance for revealing the progressive failure process and optimizing the reinforcement scheme of layered roofs in grottoes.
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