Numerical Simulation of Temperature Characteristics and Graphitization Mechanism of Diamond in Laser Powder Bed Fusion.

Thermal damage to diamonds is a major limitation in laser powder bed fusion (LPBF) processing of metal matrix diamond composites. In this paper, a numerical simulation model was established to describe the thermal effect of the Diamond-CuSn10 composite on the LPBF process. The simulation results show that the temperature of the diamond presents a double-peak structure, and the double-peak temperature curve shape can be modulated by modifying the laser scanning offset and the size of the diamond powder. And it suggests that the heat of the diamond mainly comes from the transfer of the molten pool. Then, combined with the experimental phenomenon, the mechanism of diamond graphitization in the LPBF process is analyzed. It indicates that since the surface defects of the diamond inhibit the heat conduction of the diamond, the temperature accumulates on the surface, leading to the graphitization of the diamond. Finally, based on this model, the potential of Ti-coated diamonds to prevent and reduce thermal damage in the LPBF process has been extensively studied. It is found that a Ti coating with low thermal conductivity can effectively reduce diamond temperature and improve diamond graphitization resistance. This study can provide a good method and basis for the preliminary selection of LPBF process parameters and the understanding of the graphitization mechanism of diamond tools.

[Impacts of the injection with flurphen mixture at Shenshu (BL 23) on hemodynamics and analgesia in patients with extracorporeal shock wave lithotripsy].

OBJECTIVE: To compare the differences in pain reaction, hemodynamics and clinical efficacy between extracorporeal shock wave lithotripsy (ESWL) after injection with flurphen mixture (mixture of droperidol and fentanyl citrate) at Shenshu (BL 23) and simple ESWL in the patients. METHODS: Sixty-four cases of urinary calculi with ESWL were randomized into an observation group and a control group, 32 cases in each one. In the observation group, 15 to 20 min before ESWL, flurphen mixture (droperidol injection 1.25 mg and fentanyl citrate injection 0.05 mg were diluted to 6 mL with 0.9% sodium chloride solution 4.5 mL) was injected at bilateral Shenshu (BL 23). In the control group, no any adjuvant therapy and medication were used before ESWL. The changes in blood pressure and heart rate, visual analogue scale (VAS) score, lithotripsy frequency till calculi complete removal and the rate of calculi complete removal after the first lithotripsy were observed in the two groups. RESULTS: In the control group, blood pressure and heart rate were higher during lithotripsy than those before lithotripsy (both P<0.05). In the observation group, the differences in blood pressure and heart rate were not significant statistically as compared with those before lithotripsy (both P>0.05). The blood pressure and heart rate during lithotripsy in the observation group were apparently lower than those in the control group (both P<0.05). VAS scores during lithotripsy in the observation group were lower apparently than those in the control group (both P<0.05). The lithotripsy frequency in the observation group was less than that in the control group. The rate of calculi complete removal in 1 week after the first lithotripsy in the observation group was higher than that in the control group [75.0% (24/32) vs 50.0% (16/32), P<0.05]. CONCLUSION: The flurphen mixture at Shenshu (BL 23) significantly alleviates pain reaction in patients undergoing ESWL, avoids the fluctuation of hemodynamics and improves the clinical effect of lithotripsy.

[Prevention of procedural pain in dressing changes of burn wounds by auricular injection of small-dose fentanyl].

OBJECTIVE: To explore the effective method of the prevention and treatment of procedural pain in dressing changes of burn wounds. METHODS: Ninety patients of burn injury were randomized into 3 groups, 30 cases in each one. In the group A, fentanyl citrate injection was used at corresponding injury area, jiaogan (AH6a, sympathetic nerve), fei (CO14, lung), neifenmi (CO18, endocrine) on ear, 0.25 mL at each point. In the group B, fentanyl citrate injection was applied subcutaneously in the deltoid muscle, 1 mL. In the group C, 0.9% sodium chloride injection was applied subcutaneously in the deltoid muscle, 1 mL. The visual analogue scale (VAS) was used to evaluate the analgesic effect before, during and 10 min after dressing change in the patients of the three groups separately. RESULTS: It was not different in VAS score before dressing change among the three groups (P> 0.05). Compared with that before dressing change, the pain was not significant and VAS score was not different during and after dressing change in the patients of the group A (both P>0.05), but the score in the patients of the group B and C was different significantly (all P<0.05). The VAS score during and after dressing change in the group A was lower than that in the group B and C (all P<0.05), and the score in the group B was lower than that in the group C (P<0.05). CONCLUSION: Fentanyl injection of small dose at auricular points achieves definite analgesic effect on procedural pain in dressing changes of burn wounds, superior to subcutaneous injection of fentanyl.