Fluctuating NMDA Receptor Subunit Levels in Perirhinal Cortex Relate to Their Dynamic Roles in Object Memory Destabilization and Reconsolidation

Reminder cues can destabilize consolidated memories, rendering them modifiable before they return to a stable state through the process of reconsolidation. Older and stronger memories resist this process and require the presentation of reminders along with salient novel information in order to destabilize. Previously, we demonstrated in rats that novelty-induced object memory destabilization requires acetylcholine (ACh) activity at M₁ muscarinic receptors. Other research predominantly has focused on glutamate, which modulates fear memory destabilization and reconsolidation through GluN2B- and GluN2A-containing NMDARs, respectively. In the current study, we demonstrate the same dissociable roles of GluN2B- and N2A-containing NMDARs in perirhinal cortex (PRh) for object memory destabilization and reconsolidation when boundary conditions are absent. However, neither GluN2 receptor subtype was required for novelty-induced destabilization of remote, resistant memories. Furthermore, GluN2B and GluN2A subunit proteins were upregulated selectively in PRh 24 h after learning, but returned to baseline by 48 h, suggesting that NMDARs, unlike muscarinic receptors, have only a temporary role in object memory destabilization. Indeed, activation of M₁ receptors in PRh at the time of reactivation effectively destabilized remote memories despite inhibition of GluN2B-containing NMDARs. These findings suggest that cholinergic activity at M₁ receptors overrides boundary conditions to destabilize resistant memories when other established mechanisms are insufficient.     

GRAIN SHAPE EFFECT IN SUPERPLASTIC DEFORMATION

The method controlling grain shape in TMT processing and the effect of grain shape on char-acteristic parameters in superplastic deformation were discussed.The accommodation velocityof grahl boundary sliding,which is the dominant mechanism in superplastic deformation,andthe contribution of each mechanism to the total strain,as influenced by grain shape,were ana-lyzed.Grain shape has been shown to be an essential structural factor for superplasticity.Thenan analysis was made about the effect of grain shape on the region transition strain rate sothat a new concept,critical aspect for superplasticity,was worked out.These predictions werecompared with the measured results in an Al-Zn-Mg alloy.     

针对通过噪声的空滤器声学特性研究与改进

通过实验方法分析研究了一种中型乘用车通过噪声的特性,比较该车进、排气两侧通过噪声的声级和频谱特性,确定了进气噪声对车辆进气侧通过噪声的重要影响.为了解决该车进气噪声的问题从而达到整车降噪的目的,应用实验与边界元法计算两种手段,对该车空滤器的频率响应特性进行了研究.研究发现空滤器声系统的第一阶声固有频率与进气噪声基频相耦合是造成该车辆进气侧通过噪声高于排气侧的重要原因.基于这一研究结果,在计算和实验的基础上利用Helmholtz共振腔对空滤器的声学特性进行了改进,改进后的空滤器对降低车辆进气侧通过噪声有很好的作用.     

Ni3Al中B和Mg的非平衡晶界共偏聚

在1023－1373K的初始温度和0.05-268.91K/s的冷速范围内，用Auger剖层分析确定含B和Mg的Ni3Al合金中B和Mg的非平衡晶界共偏聚行为，按照溶质－空位复合体迁移机制所导出的描述非平衡晶界偏聚的扩散速率方程解析表达式，很好地模拟了本实验结果，并确定了Ni3Al-B-Mg合金中B及B－空位复合体，Mg及Mg-空位复合体的扩散系数及复合体激活能。     

An extension of Wagner's analysis of competing scale formation

Wagner's criterion to predict the minimum concentration of solute (N _B(min) ⁰ )necessary for the exclusive formation of its scale has been modified to incorporate both thermodynamic and kinetics requirements. The analysis presented here involves a receding alloy/scale interface for which the composition of the alloy at this interface is governed by thermodynamic equilibrium between the two competing scale phases and the base alloy. This is a more rigorous analysis than that of Wagner's, who assumed the alloy/scale interface to be immobile and the solute composition at the interface to be zero. A comparison is made between values of N _B(min) ⁰ found experimentally and those predicted by Wagner's and the present criterion for a number of alloy-gas systems. It is shown that the criterion developed in the present analysis can often provide a better approximation of the actual N _B(min) ⁰ .The expressions derived from the present analysis have been extended also in a semiquantitative manner to provide a criterion for the minimum amount of solute in the alloy required for the transition from internal to external scale formation.     

晶界碳化物对Fe-Cr15-Ni25合金蠕变裂纹扩展行为的影响SCIEI

在两种不同晶界状态下研究了Fe-Cr15-Ni25合金的蠕变裂纹扩展行为。单相合金的空洞在晶界三叉点处形核,而对晶界上有碳化物析出的合金,空洞在晶界碳化物上形核。晶界碳化物阻碍了空洞的长大和连接,因而大大提高了蠕变裂纹扩展抗力。     

Monte-carlo modeling of grain growth in Zr equal channel angular pressed and recrystallized

Grain boundary character distribution in equal-channel-angular pressed Zr was studied. Using a die design of 90°/20° and an operation temperature of 350°C. The initial grain size of 20 μm was reduced to about 270 nm with 4 passes via route B_c. The grain growth kinetics of the recrystallized state was obtained by experiment and Monte-Carlo computer simulation, respectively, which showed good agreement. Based on kinetics and morphological characteristics, it was concluded that the grain coarsening mechanism was governed by normal grain growth. No sign of abnormal grain growth was detected either in the experiment or in simulation despite taking into consideration anisotropy in grain boundary energy as well as its mobility. This indicates that grain boundaries produced by severely deformed Zr are stable against explosive coarsening. The evolution characteristics of the microstructure in the present ECA pressed and recrystallized Zr differed from those of cold rolled Ti in that the grain boundary misorientation distribution and texture were rather stable during grain growth. Jointly Appointed by the Center for Advanced Aerospace Materials This article is based on a presentation made in the 2002 Korea-US symposium on the “Phase Transformations of Nano-Materials,” organized as a special program of the 2002 Annual Meeting of the Korean Institute of Metals and Materials, held at Yonsei University, Seoul, Korea on October 25–26, 2002.     

MECHANISM OF NON-EQUILIBRIUM SEGREGATION OF SOLUTE TO GRAIN BOUNDARIES

本文以空位-溶质原子拖曳机制为基础,并考虑了空位、溶质原子和复合体三者的反应平衡及晶界平衡偏聚的作用,得到了溶质原子的非平衡晶界偏聚动力学方程。对硼在奥氏体中等温及连续冷却时所产生的非平衡晶界偏聚现象进行了理论计算,得到了与实验较为一致的结果。     

钛合金中亚晶的电子显微镜观察

用透射电子显微镜观察了TC6钛合金在高温退火过程中形成的亚晶(Subgrain)。合金经850℃,920℃退火后炉冷和空冷,在初生α相晶粒内形成亚晶,多为成簇分布的狭长形状,亚晶的数量随退火后冷却速度的增加而减少。亚晶界(Subgrain boundary)是由位错构成的,亚晶的形成是多边化(polygonization)的结果。     

Ni3Al合金中晶界与位错交互作用的研究

运用嵌入原子法势函数和静态驰豫最陡梯度的计算方法,原子模拟了Ni_3Al合金中晶界与位错的交互作用.主要研究了晶界与位错交互作用的能量特征、晶界结构单元的畸变行为和晶界附近位错的核心结构,并分析讨论了各种因素对它们的影响以及与Ni_3Al晶界韧脆行为之间的关系