Raman Characterization of the In-Plane Stress Tensor of Gallium Nitride.

Experimental characterization of the in-plane stress tensor is a basic requirement for the development of GaN strain engineering. In this work, a theoretical model of stress characterization for GaN using polarized micro-Raman spectroscopy was developed based on elasticity theory and lattice dynamics. Compared with other works, the presented model can give the quantitative relationship between all components of the in-plane stress tensor and the measured Raman shift. The model was verified by a calibration experiment under step-by-step uniaxial compression. By combining the stress characterization model with the expanding cavity model, the in-plane residual stress component field around Berkovich indentation on the (0001) plane GaN was achieved. The experimental results show that the distributions of the stress components, which significantly differed from the distribution of the Raman shift, were closely related to the GaN crystal structure and exhibited a gradient along each crystal direction.

The characterization of bovine compact bone fatigue damage using terahertz spectroscopy.

Fatigue can cause cracks to propagate from the micro- to the macroscale, which results in a decrease of Young's modulus of the bone. Non-destructive measurements of bone fatigue damage are of great importance for bone quality assessment and fracture prevention. Unfortunately, there is still a lack of effective nondestructive methods sensitive to the initial deterioration during damage accumulation, particularly in the field of orthopedics and biomechanics. In this study, terahertz spectroscopy was adopted to evaluate microscale bone damage. Specifically, the refractive index and Young's modulus of bone samples subjected to different degrees of fatigue damage were tested at a fixed area. Both parameters are found to decrease in two stages under cycled fatigue loading, which is attributed to the initial onset and subsequent development of microdamage during fatigue loading. The change in refractive index reflects the accumulation of fatigue damage as well as the decrease in Young's modulus.

Modeling of Bimodular Bone Specimen under Four-Point Bending Fatigue Loading.

The fatigue damage behavior of bone has attracted significant attention in both the mechanical and orthopedic fields. However, due to the complex and hierarchical structure of bone, describing the damage process quantitively or qualitatively is still a significant challenge for researchers in this area. In this study, a nonlinear bi-modulus gradient model was proposed to quantify the neutral axis skewing under fatigue load in a four-point bending test. The digital image correlation technique was used to analyze the tensile and compressive strains during the fatigue process. The results showed that the compressive strain demonstrated an obvious two-stage ascending behavior, whereas the tensile strain revealed a slow upward progression during the fatigue process. Subsequently, a theoretical model was proposed to describe the degradation process of the elastic modulus and the movement of the neutral axis. The changes in the bone properties were determined using the FEM method based on the newly developed model. The results obtained from two different methods exhibited a good degree of consistency. The results obtained in this study are of help in terms of effectively exploring the damage evolution of the bone materials.

[Effect of Selenoprotein Thioredoxin Reductase 3 on the Survival Prognosis of Tumor Patients].

Objective To investigate the expression of thioredoxin reductase 3(TXNRD3),a selenoprotein,in 33 human malignant tumors and then analyze its effect on the survival prognosis.Methods We employed the genotype-tissue expression project database,the cancer cell line encyclopedia,and the cancer genome atlas to explore the expression of TXNRD3 gene in 33 human malignant tumors and analyze its impact on the survival prognosis.Further,we explored the correlations of TXNRD3 with immune cells and immune infiltration in the tumor microenvironment,as well as with neoantigens,immune checkpoint genes,tumor mutational burden,and microsatellite instability.Subsequently,human samples were classified into high-and low-expression groups according to TXNRD3 gene expression levels,and the enrichment analysis of biological functions and signaling pathways was performed.Results The analysis with multiple databases showed that TXNRD3 was highly expressed in 15 tumors.The survival analysis showed that TXNRD3 was significantly associated with poor prognosis in pancreatic cancer patients.In addition,the expression level of TXNRD3 was correlated with immune infiltration in tumor microenvironment,neoantigens,immune checkpoint genes,tumor mutational burden,and microsatellite instability.TXNRD3 affected the expression of DNA mismatch repair genes.The gene set enrichment indicated that TXNRD3 was involved in regulating multiple signaling pathways associated with tumor metabolism and tumor immunity.Conclusion TXNRD3 is widely expressed in tumors and has a clinical value for the survival prognosis prediction and treatment of multiple tumors,demonstrating the potential of being a promising biomarker for targeted treatment of multiple tumors.

Tensile and compressive strain evolutions of bovine compact bone under four-point bending fatigue loading.

Bones are biological composite materials with multiscale structures. Bone fatigue damage is commonly characterized by an increase in strain that is accompanied by microdamage at different scales. This study investigated the damage evolutions of bone specimens under four-point bending fatigue loading using neutral axis migration. Tensile and compressive strains during the fatigue process were simultaneously measured using a digital image correlation technique. The compressive strain of the bone specimen increased rapidly at first and then proceeded slowly while the tensile strain decreased during fatigue loading. Consequently, the neutral axis shifted downward as the damage accumulated. A positive correlation exists between the downward offset of the neutral axis and the number of cycles. The variation in compressive strain is larger than that in tensile strain in this situation.

Effects of Fatigue Damage on the Microscopic Modulus of Cortical Bone Using Nanoindentation.

Alterations to the bone structure from cycle loadings can undermine its damage resistance at multiple scales. The accumulation of fatigue damage in a bone is commonly characterized by the reduction in the elastic modulus. In this study, nano-indentation was used for investigating microscopic damage evolution of bovine tibia samples subjected to fatigue loading. Indentation tests were conducted in the same 60 µm × 120 µm area with different degrees of damage, including fracture, and the evolution of reduced modulus was observed. The results showed that bone's reduced modulus decreased significantly during the initial 40% of the life fraction, whereas it proceeded slowly during the remaining period. As the size of the residual indentations was about 4 µm in length, the degradation of bone's reduced modulus reflected the accumulation of fatigue damage at smaller scales.

A hypothetical mechanism of bone remodeling and modeling under electromagnetic loads.

A hypothetical regulation mechanism for bone modeling and remodeling under electromagnetic field is proposed. In this hypothesis, the bone modeling and remodeling mechanism is described as follows: the circular loads that we bear during ordinary daily activities generate micro-damage in cortical bone and these micro-cracks are removed by osteoclasts. Then growth factors, which are in latent forms in osteocytes, are activated by osteoclasts and released into bone fluid. These growth factors stimulate osteoblasts to refill the cavities. An electromagnetic field can stimulate the multiplication of growth factors and accelerate the bone remodeling process indirectly. It can be seen that many features reported in adaptive bone modeling and remodeling are explained by the proposed hypothesis. Further, a computational model is established based on the hypothesis, which can simulate the bone modeling and remodeling process under multi-field loads.

Thermoelectroelastic solutions for surface bone remodeling under axial and transverse loads.

Theoretical prediction of surface bone remodeling in the diaphysis of the long bone under various external loads are made within the framework of adaptive elastic theory. These loads include external lateral pressure, electric and thermal loads. Two solutions are presented for analyzing thermoelectroelastic problems of surface bone remodeling. The analytical solution that gives explicit formulation is capable of modeling homogeneous bone materials, while the semi-analytical solution is suitable for analyzing inhomogeneous cases. Numerical results are presented to verify the proposed formulation and to show the effects of mechanical, thermal and electric loads on surface bone remodeling process.