门诊25个不同民族2656例龋牙分析

<正> 龋病是口腔常见病和多发病,被世界卫生组织列为人类三种多发病之一。任何种族,任何年龄,任何性别,皆可罹患。在我国山顶洞人的头骨上,就发现有龋牙以及由龋病而引起的颌骨破坏,在殷墟及战国时期的头骨上,可看到龋牙已较普遍。关于龋病的文字记载,在殷墟甲骨文即有发现,而在《史记·仓公传》中,则有龋病的病例报告。我国幅员广大,地域辽阔,各地物质文化生活条件、地理环境和饮食习惯不同,龋患率也不相同,大体上南方和沿海一带龋患率较高,而西北内地则较低,此外,不同民族的民俗     

Co2VZ(Z=Ga,Si)合金马氏体相变的第一性原理计算

计算不同磁有序下的相稳定性及弹性常数对实验上设计具有良好性能的Co2VZ(Z=Ga,Si)基形状记忆合金具有重要意义.采用精确Muffin-T in轨道结合相干势近似方法,系统计算了0K下Co2VZ基合金立方奥氏体和四方马氏体相的品格结构、磁矩、弹性常数及总能.结果 表明,在FM状态下,Co2VGa具有L21立方结构,...     

Alloying and magnetic disordering effects on phase stability of Co2 YGa (Y=Cr,V, and Ni) alloys: A first-principles study

The alloying and magnetic disordering effects on site occupation, elastic property, and phase stability of Co$_{2}Y$Ga ($Y={\rm Cr}$, V, and Ni) shape memory alloys are systematically investigated using the first-principles exact muffin-tin orbitals method. It is shown that with the increasing magnetic disordering degree $y$, their tetragonal shear elastic constant $C'$ (i.e., $(C_{11}-C_{12})/2$) of the $L2_{1}$ phase decreases whereas the elastic anisotropy $A$ increases, and upon tetragonal distortions the cubic phase gets more and more unstable. Co$_{2}$CrGa and Co$_{2}$VGa alloys with $y\geq0.2$ thus can show the martensitic transformation (MT) from $L2_{1}$ to $D0_{22}$ as well as Co$_{2}$NiGa. In off-stoichiometric alloys, the site preference is controlled by both the alloying and magnetic effects. At the ferromagnetism state, the excessive Ga atoms always tend to take the $Y$ sublattices, whereas the excessive Co atom favor the $Y$ sites when $Y={\rm Cr}$, and the excessive $Y$ atoms prefer the Co sites when $Y={\rm Ni}$. The Ga-deficient $Y={\rm V}$ alloys can also occur the MT at the ferromagnetism state by means of Co or V doping, and the MT temperature $T_{\rm M}$ should increase with their addition. In the corresponding ferromagnetism $Y={\rm Cr}$ alloys, nevertheless, with Co or Cr substituting for Ga, the reentrant MT (RMT) from $D0_{22}$ to $L2_{1}$ is promoted and then $T_{\rm M}$ for the RMT should decrease. The alloying effect on the MT of these alloys is finally well explained by means of the Jahn-Teller effect at the paramagnetic state. At the ferromagnetism state, it may originate from the competition between the austenite and martensite about their strength of the covalent banding between Co and Ga as well as $Y$ and Ga.     

运动性牙损伤的探讨

<正> 运动员无论是训练或比赛,在颌面部创伤中常伴有牙齿损伤,尤以上、下颌前牙位于牙弓前缘突出部分;即垣上中切牙及侧切牙最易受损伤。一般可分为牙碰伤、牙脱位、牙折断三种。一、牙碰伤:牙碰伤可发生在于直接和间接的暴力作用下,如运动员运动时的冲撞,或在面向下跌跤与急行向外扑时,或在进食时聚然咀嚼小硬块碎骨、砂粒等,皆可引起牙碰     

磁无序及合金化效应影响Co2CrZ(Z=Ga,Si,Ge)合金相稳定性和弹性常数的第一性原理研究

采用确切的Muffin-Tin轨道结合相干势近似方法,本文系统计算研究了0 K下,磁无序及合金化效应影响Co₂CrZ(Z=Ga,Si,Ge)合金L2₁和DO₂₂相稳定性的规律性及物理机理.研究结果表明,0 K下,L2₁相合金晶格常数、体弹性模量、磁矩和弹性常数均与理论和实验值基本吻合;铁磁下合金具有L2₁结构,随磁无序度(y)的增大,L2₁相能量相对逐渐增大,最终由低于转变到高于D0₂₂相,因此,当y≥0.1(0.2)时,Z=Si和Ge(Z=Ga)的合金具有DO₂₂相稳定结构;随y的增大,L2₁相的四方剪切弹性模量(C’=(C₁₁-C₁₂)/2)还不断软化,表明无论在能量还是力学角度上,磁无序都有利于3种合金发生四方晶格变形;磁无序影响L2₁和D0₂₂相相对稳定性的电子结构机理归因于Jahn-Teller...