Shear Bond Strength of Different Types of Cement Used for Bonding Band and Loop Space Maintainer

Purpose: The present study aimed to evaluate the effects of thermal aging on the shear bond strength of three different types of cement used to retain band and loop space maintainers cemented on extracted human permanent molar teeth. Methods: A total of 66 newly extracted permanent molars were used in this study. Eighteen teeth were used as a control and did not undergo thermal aging (six per group). All sample teeth were randomly divided into three groups: KetacCem, RelyX Luting Plus, and RelyX Unicem 2. After bonding procedures, all experimental groups undergo thermal aging. The shear bond strength of all samples was conducted using the Ultratester machine. Findings were statistically analyzed using the ANOVA and Turkey’s post hoc tests. Results: Among the examined groups, Ketac Cem presented with the highest recorded shear bond (11.4 MPa), while RelyX Luting Plus showed the lowest (3.2 MPa). The control groups recorded the highest shear bond strength compared to all examined groups;Ketac Cem showed the highest shear bond strength (12.8 Mpa), and RelyX Luting Plus had the least recorded reading (5.4 Mpa). Conclusion: Within the limitation of the present study, there was a statistically significant difference between the examined groups;Ketac Cem showed a higher shear bond cement than RelyX luting Plus and RelyX Unicem.

A novel high precision Doppler frequency estimation method based on the third-order phase-locked loop

In deep space exploration,many engineering and scientific requirements require the accuracy of the measured Doppler frequency to be as high as possible.In our paper,we analyze the possible frequency measurement points of the third-order phase-locked loop(PLL)and find a new Doppler measurement strategy.Based on this finding,a Doppler frequency measurement algorithm with significantly higher measurement accuracy is obtained.In the actual data processing,compared with the existing engineering software,the accuracy of frequency of 1 second integration is about 5.5 times higher when using the new algorithm.The improved algorithm is simple and easy to implement.This improvement can be easily combined with other improvement methods of PLL,so that the performance of PLL can be further improved.

Actads

In this paper,I introduce a new generalization of the concept of an operad,further generalizing the concept of an opetope introduced by Baez and Dolan(1998),who used this for the definition of their version of non-strict n-categories.Opetopes arise from iterating a certain construction on operads called the+-construction,starting with monoids.The first step gives rise to plain operads,i.e.,operads without symmetries.The permutation axiom in a symmetric operad,however,is an additional structure resulting from permutations of variables,independent of the structure of a monoid.Even though we can apply the+-construction to symmetric operads,there is the possibility of introducing a completely different kind of permutations on the higher levels by again permuting variables without regard to the structures on the previous levels.Defining and investigating these structures is the main purpose of this paper.The structures obtained in this way are what I call n-actads.In n-actads with n>1,the permutations on the different levels give rise to a certain special kind of n-fold category.I also explore the concept of iterated algebras over an n-actad(generalizing an algebra and a module over an operad),and various types of iterated units.I give some examples of algebras over 2-actads,and show how they can be used to construct certain new interesting homotopy types of operads.I also discuss a connection between actads and ordinal notation.