目的:比较断冠再接和复合树脂直接修复两种方法修复前牙冠折后剪切力的差异。方法:制备恒上颌中切牙不累及髓腔的冠折模型36个,随机分为A、B组(n=18),A组采用自酸蚀粘结剂Clearfil SE Bond进行断冠再接,B组采用Clearfil SE Bond和复合树...目的:比较断冠再接和复合树脂直接修复两种方法修复前牙冠折后剪切力的差异。方法:制备恒上颌中切牙不累及髓腔的冠折模型36个,随机分为A、B组(n=18),A组采用自酸蚀粘结剂Clearfil SE Bond进行断冠再接,B组采用Clearfil SE Bond和复合树脂Clearfil AP-X进行直接修复。修复24 h后置于万能试验机加载台上,持续加载、直至折断,并记录折断时的力值。结果:断冠再接和复合树脂直接修复后的剪切力(N)分别为326.78±70.66和351.74±54.11(t=1.190,P=0.242)。结论:断冠再接和复合树脂直接修复两种方法修复前牙冠折后剪切力无明显差异。展开更多
For years,friction-induced vibration and noise(FIVN)has puzzled many researchers in academia and industry.Several mechanisms have been proposed for explaining its occurrence and quantifying its frequencies,notably for...For years,friction-induced vibration and noise(FIVN)has puzzled many researchers in academia and industry.Several mechanisms have been proposed for explaining its occurrence and quantifying its frequencies,notably for automotive brake squeal,clutch squeal,and even rail corrugation.However,due to the complex and complicated nature of FIVN,there is not yet one fundamental mechanism that can explain all phenomena of FIVN.Based on experimental results obtained on a simple test structure and corresponding numerical validation using both complex eigenvalue analysis(CEA)and transient dynamic analysis(TDA),this study attempts to propose a new fundamental mechanism for FIVN,which is the repeated cycles of partial detachment and then reattachment of the contact surfaces.Since friction is ubiquitous and FIVN is very common,the insight into FIVN reported in this paper is highly significant and will help establish effective means to control FIVN in engineering and daily life.展开更多
The present study deals with the study of the velocity distribution and the separation phenomenon of flow of air over a two dimensional backward facing step. The flow of air over a backward facing step has been invest...The present study deals with the study of the velocity distribution and the separation phenomenon of flow of air over a two dimensional backward facing step. The flow of air over a backward facing step has been investigated numerically using FLUENT. Flow simulation has been carried out in a backward facing step having an expansion ratio （ratio of the height before and after the step） of 1：1.94 and the results obtained are compared with the published experimental results. Comparison of flow characteristics between steps with three different transitions is made. The variation ofreattachment length for all the three cases are analyzed for wide range of Reynolds number ranging from 100 to 7000 which covers the laminar, transition and turbulent flow of air. Simulation of the flow over steps with expansion ratios of 1：1.24, 1：1.38, 1：1.47, 1：1.53, 1：1.94, 1：2.20 are also carried out to examine the effect of different expansion ratios on the reattachment length. It is found that the primary reattachment length increases with increase in the expansion ratio. The primary reattachment length at the bottom wall downstream of the step is minimum for the step with round edged transition and maximum for the step with a vertical drop transition.展开更多
文摘目的:比较断冠再接和复合树脂直接修复两种方法修复前牙冠折后剪切力的差异。方法:制备恒上颌中切牙不累及髓腔的冠折模型36个,随机分为A、B组(n=18),A组采用自酸蚀粘结剂Clearfil SE Bond进行断冠再接,B组采用Clearfil SE Bond和复合树脂Clearfil AP-X进行直接修复。修复24 h后置于万能试验机加载台上,持续加载、直至折断,并记录折断时的力值。结果:断冠再接和复合树脂直接修复后的剪切力(N)分别为326.78±70.66和351.74±54.11(t=1.190,P=0.242)。结论:断冠再接和复合树脂直接修复两种方法修复前牙冠折后剪切力无明显差异。
基金the National Natural Science Foundation of China(No.11672052)Natural Science Foundation of Zhejiang Province(LQ22E050012)are gratefully acknowledged.
文摘For years,friction-induced vibration and noise(FIVN)has puzzled many researchers in academia and industry.Several mechanisms have been proposed for explaining its occurrence and quantifying its frequencies,notably for automotive brake squeal,clutch squeal,and even rail corrugation.However,due to the complex and complicated nature of FIVN,there is not yet one fundamental mechanism that can explain all phenomena of FIVN.Based on experimental results obtained on a simple test structure and corresponding numerical validation using both complex eigenvalue analysis(CEA)and transient dynamic analysis(TDA),this study attempts to propose a new fundamental mechanism for FIVN,which is the repeated cycles of partial detachment and then reattachment of the contact surfaces.Since friction is ubiquitous and FIVN is very common,the insight into FIVN reported in this paper is highly significant and will help establish effective means to control FIVN in engineering and daily life.
文摘The present study deals with the study of the velocity distribution and the separation phenomenon of flow of air over a two dimensional backward facing step. The flow of air over a backward facing step has been investigated numerically using FLUENT. Flow simulation has been carried out in a backward facing step having an expansion ratio （ratio of the height before and after the step） of 1：1.94 and the results obtained are compared with the published experimental results. Comparison of flow characteristics between steps with three different transitions is made. The variation ofreattachment length for all the three cases are analyzed for wide range of Reynolds number ranging from 100 to 7000 which covers the laminar, transition and turbulent flow of air. Simulation of the flow over steps with expansion ratios of 1：1.24, 1：1.38, 1：1.47, 1：1.53, 1：1.94, 1：2.20 are also carried out to examine the effect of different expansion ratios on the reattachment length. It is found that the primary reattachment length increases with increase in the expansion ratio. The primary reattachment length at the bottom wall downstream of the step is minimum for the step with round edged transition and maximum for the step with a vertical drop transition.
