In Vivo Degradation Behavior of Magnesium Alloy for Bone Implants with Improving Biological Activity, Mechanical Properties, and Corrosion Resistance.

This study aimed to establish a surface modification technology for ZK60 magnesium alloy implants that can degrade uniformly over time and promote bone healing. It proposes a special micro-arc oxidation (MAO) treatment on ZK60 alloy that enables the composite electrolytes to create a coating with better corrosion resistance and solve the problems of uneven and excessive degradation. A magnesium alloy bone screw made in this way was able to promote the bone healing reaction after implantation in rabbits. Additionally, it was found that the MAO-treated samples could be sustained in simulated body-fluid solution, exhibiting excellent corrosion resistance and electrochemical stability. The Ca ions deposited in the MAO coating were not cytotoxic and were beneficial in enhancing bone healing after implantation.

Temperature prediction of ultrasonic vibration-assisted milling.

Machining temperature is a key factor in ultrasonic vibration-assisted milling as it can significantly influence tool wear rate and residual thermal stresses. In current study, a physics-based analytical predictive model on machining temperature in ultrasonic vibration-assisted milling is proposed, without resorting to iterative numerical simulations. As the tool periodically loses contact with the workpiece under vibration, three types of tool-workpiece separation criteria are first examined based on the tool trajectory under ultrasonic vibration. Type I criterion examines whether the relative velocity between tool and workpiece in cutting direction is opposite to the tool rotation direction. Type II criterion examines whether the instantaneous vibration displacement in radial direction is larger than instantaneous uncut chip thickness. Type III criterion examines whether there is overlap between current and previous tool paths due to vibration. If no contact, the instantaneous temperature rise is zero. Otherwise, the temperature rise is predicted under shearing heat source in shear zone and secondary rubbing heat source along machined surface. A mirror heat source method is applied to predict temperature rise, considering oblique band heat sources moving in a semi-infinite medium. The proposed predictive temperature model in ultrasonic vibration-assisted milling is validated through comparison to experimental measurements on Al 6063 alloy. The proposed predictive model is able to match the measured temperature with high accuracy of 1.85% average error and 5.22% largest error among all cases. Sensitivity analysis is also conducted to study the influences of cutting and vibration parameters on temperature. The proposed model is valuable in terms of providing an accurate and reliable reference for the prediction of temperature in ultrasonic vibration-assisted milling.

Influence of Inherent Surface and Internal Defects on Mechanical Properties of Additively Manufactured Ti6Al4V Alloy: Comparison between Selective Laser Melting and Electron Beam Melting.

Additive manufacture (AM) appears to be the most suitable technology to produce sophisticated, high quality, lightweight parts from Ti6Al4V alloy. However, the fatigue life of AM parts is of concern. In our study, we focused on a comparison of two techniques of additive manufacture-selective laser melting (SLM) and electron beam melting (EBM)-in terms of the mechanical properties during both static and dynamic loading. All of the samples were untreated to focus on the influence of surface condition inherent to SLM and EBM. The EBM samples were studied in the as-built state, while SLM was followed by heat treatment. The resulting similarity of microstructures led to comparable mechanical properties in tension, but, due to differences in surface roughness and specific internal defects, the fatigue strength of the EBM samples reached only half the value of the SLM samples. Higher surface roughness that is inherent to EBM contributed to multiple initiations of fatigue cracks, while only one crack initiated on the SLM surface. Also, facets that were formed by an intergranular cleavage fracture were observed in the EBM samples.

Sun tracking systems: a review.

The output power produced by high-concentration solar thermal and photovoltaic systems is directly related to the amount of solar energy acquired by the system, and it is therefore necessary to track the sun's position with a high degree of accuracy. Many systems have been proposed to facilitate this task over the past 20 years. Accordingly, this paper commences by providing a high level overview of the sun tracking system field and then describes some of the more significant proposals for closed-loop and open-loop types of sun tracking systems.

High performance microfluidic capillary electrophoresis devices.

This paper presents a novel microfluidic capillary electrophoresis (CE) device featuring a double-T-form injection system and an expansion chamber located at the inlet of the separation channel. This study addresses the principal material transport mechanisms depending on parameters such as the expansion ratio, the expansion length, the fluid flow. Its design utilizes a double-L injection technique and combines the expansion chamber to minimize the sample leakage effect and to deliver a high-quality sample plug into the separation channel so that the detection performance of the device is enhanced. Experimental and numerical testing of the proposed microfluidic device that integrates an expansion chamber located at the inlet of the separation channel confirms its ability to increase the separation efficiency by improving the sample plug shape and orientation. The novel microfluidic capillary electrophoresis device presented in this paper has demonstrated a sound potential for future use in high-quality, high-throughput chemical analysis applications and throughout the micro-total-analysis systems field.

Experimental and numerical investigation into leakage effect in injectors of microfluidic devices.

This paper performs an experimental and numerical investigation into low-leakage injectors designed for electrophoresis microchips. The principal material transport mechanisms of electrokinetic migration, fluid flow, and diffusion are considered in developing a mathematical model of the electrophoresis process. Low-leakage injectors designed with injection channels orientated at various included angles are designed and tested. The numerical and experimental results indicate that the injector with a 30 degrees included angle successfully minimizes sample leakage and has an exciting potential for use in high-quality, high-throughput chemical analysis procedures and in many other applications in the field of micro-total analysis systems.