In China many women in labor are young primigravidas whose fear of labor pain leads them to request cesarean deliveries. While the rate of cesarean deliveries has reached 50% in many hospitals, less than 1% of women in labor are given neuraxial analgesia. The necessary equipment is seldom available in China and many physicians have misconceptions about the risks associated with neuraxial analgesia, which are low with the ultra-low-dosages used today. However, attitudes have begun to change. Meetings held in China have brought together Chinese physicians and world experts on the various epidural and combined spinal-epidural techniques. Thanks to the information and support provided at these meetings clinical trials were carried out, more than 5000 women benefited from labor analgesia, and publications appeared in Chinese journals. An effective, safe, and cost-effective way to provide analgesia to women in labor may slow the increase in cesarean delivery rates across China and improve women's health in general.
The lost foam process is capable of making castings with extremely complicated shapes at high soundness levels and with low manufacturing costs. However, there are several challenges to produce magnesium castings using the conventional lost foam process because of the low heat content of magnesium alloys. Therefore, a novel low pressure lost foam process has been developed especially for magnesium castings, in which the melt is filled under counter gravity conditions at low pressure. This paper introduces the low pressure lost foam process. The measurement of flow profiles in the plate shape and the L shape EPS patterns under different conditions reveals that the process can offer unique advantages for achieving laminar flow and fully controlled flow during melt filling. The dimensional accuracy with the specially designed castings shows that CT4-8 is achievable for magnesium castings produced by the low pressure lost foam process, according to the dimensional tolerance grading given in ISO8062-1994. A comparison and Weibull statistics analysis of the mechanical properties of AZ91E alloy confirms that the low pressure lost foam process gives comparable yield strength, ultimate tensile strength, and elongation to the conventional precision sand process.
The effects of Cu addition on microstructure, mechanical properties and damping capacity of Mg-3%Ni based alloy were investigated by using tensile tests, X-ray diffraction, scanning electron microscope and dynamic mechanical analyzer. The results show that Cu addition could reduce the size of -Mg dendrites and a new binary phase Mg2Cu can be identified, which mostly distributes among the inter-dendrites in the form of typical lamellar-like eutectic microstructure and improve the mechanical properties. In low strain amplitude, with the increase of Cu addition, the damping capacities of Cu contained alloys change little, while in high strain range, the internal friction values decrease gradually with the grain refinement and increasing content of eutectic phase.
The influence of Y on the microstructure and damping capacity of AZ91D based alloys was investigated by optical microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and dynamic mechanical analysis. The results show that, with increasing Y content, the grain size of α-Mg matrix decreases tremendously and the distribution of β-Mg17Al12 phase is transformed from discontinuous network to fine particles. Meanwhile, a needle-shaped Al4MgY phase mainly distributing at the grain boundaries is identified. The damping capacity of the studied alloys shows sustained enhancement with increasing temperature. As to the strain dependent damping capacity, with the increase of Y content, the damping value of AZ91D alloy decreases gradually before Y content reaches to 0.5wt.%, and fluctuates when Y addition is between 0.5wt.%~0.9wt.%. G-L dislocation model was employed to explain the effects of parameters on damping capacity of magnesium alloy.
In this study, three dimensional structures are fabricated by a self-developed three dimensional printing machine with eight different particle size distribution scrubbed silica sand. In order to evaluate particle size distribution effect on the properties of sand mold, the physical and mechanism properties of printed specimens, including weight, gas evolution, air permeability, tensile strength and compressive strength, were measured. The mechanism of effect was analyzed and studied. The results show that the printed specimens from the 80-140 mesh sand powder have the best comprehensive properties. Both wider and narrower particle size distribution adversely affects the properties of printed specimens.
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