Repeated Loading Model for Elastic-Plastic Contact of Geomaterial

A new nonlinear hysteretic model with considering the loading, unloading, and reloading processes is developed based on Drucker—Prager yield criterion and finite-element analysis. This model can be used for multiple repeated elastic—plastic normal direction contact problems between two identical spherical geomaterials. After examining the influence of material properties, strain hardening, and loading histories, we found that the hysteretic phenomena (represented by residual displacement and plastic work) become weak after the first cycle, and the subsequent cycles step into elastic shakedown state eventually. A critical number of cycles can be used to estimate the state of ratchetting, plastic shakedown, as well as elastic shakedown. It also found that the subsequent curves will be stiffer than the previous ones, especially when the yield strength is high and ratchetting effect is not strong. This new model can be used for a wide range of geomaterials under different loading levels, and it can also be extended to describe the constitutive behavior of spheres under earthquake as well as aftershocks

A Simple Model for Elastic-Plastic Contact of Granular Geomaterials

We propose a simple elastic-plastic contact model by considering the interaction of two spheres in the normal direction, for use in discrete element method (DEM) simulations of geomaterials. This model has been developed by using the finite element method (FEM) and nonlinear fitting methods, in the form of power-law relation of the dimensionless normal force and displacement. Only four parameters are needed for each loading-unloading contact process between two spheres, which are relevant to material properties evaluated by FEM simulations. Within the given range of material properties, those four parameters can be quickly accessed by interpolating the data appended or by regression functions supplied. Instead of the Von Mises (V-M) yield criterion, the Drucker-Prager (D-P) criterion is used to describe the yield behavior of contacting spheres in this model. The D-P criterion takes the effects of confining pressure, the intermediate principal stress, and strain rate into consideration; thus, this model can be used for DEM simulation of geomaterials as well as other granular materials with pressure sensitivity

Finite Element Analysis of the Wear Fatigue of Rails with Gradient Structures

We performed the finite element modeling for the first time to analyze the effect of gradient structures (GS) on the wear fatigue-resistant of rails in the rolling-sliding contacts. We found that GS can enhance the wear fatigue-resistant of rails by reducing the maximum horizontal and vertical displacements on the surface of rails. The thicker GS layers, the better the performance is. For a fixed GS layer thickness, increasing the surface yield strength can effectively reduce surface displacements. The outcome from this study can provide the design guideline for processing the gradient structures in the rail steels to obtain superior mechanical properties

Analysis of the Water-Energy Coupling Efficiency in China: Based on the Three-Stage SBM-DEA Model with Undesirable Outputs

Although the relationships between water and energy systems have been widely researched globally, such studies have not properly considered the coupling and driving mechanisms of the nexus between water and energy. Based on panel data from 30 Chinese provinces and cities, we used a three-stage Slacks-Based Measure model for Data Envelopment Analysis (SBM-DEA) to estimate the Water-Energy coupling efficiency in China from 2003–2015. Using the Stochastic Frontier Approach (SFA) regression model, we constructed an index of environmental factors that affect the Water-Energy coupling efficiency from the four aspects of resource environment, social environment, economic environment, and ecological environment. The results indicate that the Water-Energy coupling efficiency scores in most provinces in China are high and stable, and that the coupling efficiency of water and energy in China has a distribution pattern of northeast > east > west > central. Compared to the results in the first stage of analysis, the efficiency values in the third stage (after removal of environmental and stochastic factors) were smaller, illustrating that the coupling efficiency of water and energy in China depends on a favorable external environment. In the sample period, we also found that the improvement of the resource and social environments was the most conducive way to improve the Water-Energy coupling efficiency. Overall, the management level of technological innovation in China still has some room for improvement

Crystal Plasticity Modeling of Fretting Fatigue Behavior of an Aluminum Alloy

Aluminum alloy (AA)7075 is widely used to fabricate parts and components on aircrafts, which are subjected to contact loading that may induce fretting fatigue and catastrophic failure. In this work, a crystal plasticity finite element (CPFE) model accounting for the microstructural features is developed for simulating the fretting fatigue of AA7075-T651. A submodel technology is adopted to refine the contact region to obtain more accurate simulation data. An energy-based criterion is developed for prediction of crack initiation life. The hotspots for the fretting fatigue crack nucleation are identified by the maximum of plastic strain energy density. The proposed CPFE model achieves high accuracy on predicting the fretting fatigue crack initiation and validated by fretting fatigue experimental results

Image-Based Adaptive Staring Attitude Control for Multiple Ground Targets Using a Miniaturized Video Satellite

A miniaturized video satellite can observe the ground targets by recording real-time video clips in staring control mode and therefore obtains a unique advantage over traditional remote sensing techniques. To further extend the application of a video satellite, a strategy for simultaneously observing a group of ground targets is to be developed. To cope with the impacts of an uncalibrated camera on the pointing accuracy which can lead to the failure of a multi-target observation task, an adaptive attitude control method is to be exploited. Hence, to observe multiple ground targets using an onboard uncalibrated camera, this paper proposes an image-based adaptive staring attitude controller. First, a target-selection strategy is proposed to realize a more balanced staring observation of the target group. Second, an updating law is proposed to estimate the camera parameters according to the projection equations. At last, an adaptive staring controller based on the estimated parameters is formulated, so that the center of mass of the ground targets on the image can be controlled towards its desired location, which is normally the image center. The stability of the proposed staring controller is proved using Barbalat’s Lemma. The simulation results show that even though the camera parameters are uncertain, the adaptive control method effectively achieves the staring observation for multiple ground targets by keeping their midpoint at the image center

Effect of Plastic Incompatibility on the Strain Hardening Behavior of Al-TiN Nanolayered Composites

The strain hardening behavior of Al-TiN nanolayered composites induced by plastic incompatibility was studied by 3-D discrete dislocation dynamics (DDD) simulations. Our simulations results indicate the strain hardening rate solely induced by the plastic incompatibility is independent of layer thickness and dislocation density at a constant layer thickness ratio, while the yield stress exhibits a strong size effect. Furthermore, the strain hardening rate increases with decreasing Al/TiN layer thickness ratio and our predicted results match well with prior experiment data

Bench-to-bedside: Translational development landscape of biotechnology in healthcare

Biotechnology is a rapidly evolving field that has the potential to transform the way we diagnose and treat diseases and is changing the landscape of healthcare. Great endeavors have been devoted to the field of healthcare biotechnology, and our knowledge of the subject has remarkably improved. By leveraging the latest advancements in molecular biology and genetics, new biotech paradigms are emerging, sparking new searches for novel solutions for human health and well-being. However, the clinical translational development of breakthrough biotechnology discoveries remains an intriguing challenge. Only a few biotech innovations have progressed to new transformative healthcare tools and therapies. In this review, we will outline the clinical translational development landscape of biotechnology in healthcare. Notable discoveries and translational developments in healthcare biotechnology, including classical discoveries and new paradigms, are thoroughly discussed. Even though great challenges remain in the bench-to-bedside translational development process, more groundbreaking biotech ideas are about to be translated into commercial products to bring positive health gains, with a tight multitude of collaboration among research institutes, healthcare providers, and industry partners

Productivity-Index Behavior for a Horizontal Well Intercepted by Multiple Finite-Conductivity Fractures Considering Nonlinear Flow Mechanisms under Steady-State Condition

In this paper, a mathematical model is proposed to investigate the effect of nonlinear flow mechanisms on productivity-index (PI) behavior in hydraulically fractured reservoirs during steady-state condition. This approach focuses on the fact that PI approaches a constant value at a certain time, indicating the beginning of steady state. In this model, the reservoirs are considered as an elliptical-shaped drainage with constant-pressure boundary, which is depleted by a multiple-fractured horizontal well (MFHW), and various nonlinear flow mechanisms, such as the non-Darcy flow effect and pressure-dependency effect, control flow patterns in the hydraulic fractures. Then, an exact algorithm of solving the resulting nonlinear equations is developed to obtain the PI of MFHW using a semi-analytical approach. Next, type curves are generated to investigate the influences of flow mechanisms and fracture properties on PI. The most interesting points in this study are the following: (1) PI is determined by the properties of MHFW (i.e., dimensions and configuration), the reservoir geometry, and flow mechanism; (2) PI is deteriorated by non-Darcy flow caused by inertial forces; and (3) PI is reduced under the influence of pressure sensitivity caused by the degradation of dynamic conductivity. Generally, this study provides a significant insight into understanding the factors affecting the productivity of a MFHW with nonlinear flow mechanisms