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Bone metabolism occurs in the entire life of an individual and is required for maintaining skeletal homeostasis. The imbalance between osteogenesis and osteoclastogenesis eventually leads to osteoporosis. Oxidative stress is considered a major cause of bone homeostasis disorder, and relieving excessive oxidative stress in bone mesenchymal stem cells (BMSCs) is a potential treatment strategy for osteoporosis. Carbon monoxide releasing molecule-3 (CORM-3), the classical donor of carbon monoxide (CO), possesses antioxidation, antiapoptosis, and anti-inflammatory properties. In our study, we found that CORM-3 could reduce reactive oxygen species (ROS) accumulation and prevent mitochondrial dysfunction thereby restoring the osteogenic potential of the BMSCs disrupted by hydrogen peroxide (H2O2) exposure. The action of CORM-3 was preliminarily considered the consequence of Nrf2/HO-1 axis activation. In addition, CORM-3 inhibited osteoclast formation in mouse primary bone marrow monocytes (BMMs) by inhibiting H2O2-induced polarization of M1 macrophages and endowing macrophages with M2 polarizating ability. Rat models further demonstrated that CORM-3 treatment could restore bone mass and enhance the expression of Nrf2 and osteogenic markers in the distal femurs. In summary, CORM-3 is a potential therapeutic agent for the treatment of osteoporosis.

This chapter is devoted to using the loop‐breaking 2 (LB 2) method to solve a two‐level voltage source converter (VSC). An example of a dc‐dc buck converter is used to demonstrate how augmented matrix methods can be easily incorporated into the LB 2 method, which avoids evaluating convolution integrals. To obtain the expressions for the VSC, the open‐loop equations, consisting of both the power converter and the controllers for the VSC, need to be formulated. The chapter demonstrates how a VSC, whose controllers are described in the dq frame, can also be modeled by the LB 2 method. It presents different case studies to compare the number of unknown variables required to simulate a two‐level VSC based on the LB 1 and LB 2 methods, under different switching frequencies. Finally, the chapter shows how a line‐commutated power converter can be modeled by means of the LB 2 method.

Power electronics is the technology of converting electric power from one form to another using electronic power devices. This chapter briefly discusses the types of semiconductor switches and their functionalities. Moreover, types of power electronic converters such as voltage source converter and current source converter are briefly discussed. Power electronic devices generally consist of static switches, which are in general made of semiconductor material. The electronic bandgap is the energy gap between the top of the valence band and the bottom of the conduction band in solid materials. The static switches discussed can only conduct current in one direction, while the voltage blocking capability of some switches can be both directions. These basic switches can be used to construct more sophisticated switches. One widely used approach to the categorization of converters is based on the commutation process.

A numerical method is a mathematical tool designed to solve numerical problems. The implementation of a numerical method in a programming language is called a numerical algorithm. This chapter provides a basic review of some of the commonly used iterative numerical algorithms for solving nonlinear problems. It briefly goes through the algorithms of Gauss–Seidel, predictor‐corrector, Newton’s method, and the particle swarm optimization algorithm. The chapter also summarizes the approximate errors for Gauss–Seidel and Newton’s methods. It clearly shows that the error of Newton’s method decreases quadratically (square of the error) whereas that of the Gauss–Seidel method decreases linearly. Newton’s method is a very powerful method as the convergence of the solution is quadratic, which means that the difference between the root and the approximation is squared at each iteration step.

This chapter is devoted to the elaboration of the loop‐breaking 3 (LB 3) method where the loop breaking is occurred within and between components. It shows how the LB 3 method can be applied to solve for a power system containing multiple voltage source converters (VSCs). OpenDSS serves as an ideal platform for the LB 3 method. The chapter briefly describes OpenDSS and shows how the MATLAB program can be interfaced with OpenDSS. In order to represent the VSC models as harmonic current sources in OpenDSS, the current harmonics need to be expressed as the per unit value of the fundamental current harmonic and are represented as an inherited property, spectrum. The chapter illustrates various examples on how developed VSC models can be interfaced with OpenDSS.

The impact toughness of powder metallurgy (PM) steel is typically inferior, and it is further impaired when the microstructure is strengthened. To formulate a versatile PM steel with superior impact, fatigue, and tensile properties, the influences of various microstructures, including ferrite, pearlite, bainite, and Ni-rich areas, were identified. The correlations between impact toughness with other mechanical properties were also studied. The results demonstrated that ferrite provides more resistance to impact loading than Ni-rich martensite, followed by bainite and pearlite. However, Ni-rich martensite presents the highest transverse rupture strength (TRS), fatigue strength, tensile strength, and hardness, followed by bainite, pearlite, and ferrite. With 74 pct Ni-rich martensite and 14 pct bainite, Fe-3Cr-0.5Mo-4Ni-0.5C steel achieves the optimal combination of impact energy (39 J), TRS (2170 MPa), bending fatigue strength at 2 × 106 cycles (770 MPa), tensile strength (1323 MPa), and apparent hardness (38 HRC). The impact energy of Fe-3Cr-0.5Mo-4Ni-0.5C steel is twice as high as those of the ordinary high-strength PM steels. These findings demonstrate that a high-strength PM steel with high-toughness can be produced by optimized alloy design and microstructure.