Reciprocal Associations Between Adolescent Sexual Activity and Quality of Youth-Parent Interactions.

The authors examined differences in adolescents' relationships with their parents before and after adolescent first sexual activity. Participants were 13,570 members of the core sample of the National Longitudinal Survey of Adolescent Health (Add Health) Waves 1 and 2. Path analyses examined changes in parent-adolescent closeness, shared activities, and problem-focused interactions associated with changes in sexual activity separately for sons and daughters and for mothers and fathers. Race, religion, age, urbanicity, and parents' education were controls. Results confirm that increased problem-focused interactions and decreased parental closeness and shared activities both precede and follow adolescent sexual activity. Maintaining positive parental relations after adolescent first sexual activity is discussed as a means to reduce risks associated with sex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multivariate Modeling of Age and Retest in Longitudinal Studies of Cognitive Abilities.

Longitudinal multivariate mixed models were used to examine the correlates of change between memory and processing speed and the contribution of age and retest to such change correlates. Various age- and occasion-mixed models were fitted to 2 longitudinal data sets of adult individuals (N > 1,200). For both data sets, the results indicated that the correlation between the age slopes of memory and processing speed decreased when retest effects were included in the model. If retest effects existed in the data but were not modeled, the correlation between the age slopes was positively biased. The authors suggest that although the changes in memory and processing speed may be correlated over time, age alone does not capture such a covariation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

四川锦屏山电站施工辅助洞通风设计方案分析

四川锦屏山电站施工辅助隧道属特长隧道,本文根据其特殊性,重点比较了目前常用的几种隧道通风方式,最终选择一种较为合理的通风方案.     

Solvent Extraction Calculation Model for Purex Process in Pulsed Sieve Plate Column

A new calculation code PULCO has been developed to simulate the Purex extraction process in a pulsed column. The model for the PULCO code is based on the mass transfer taking place at the interface between dispersed drops and continuous phase fluid. The following physical quantities of the moving drop are included in the model for each period of drop motion in a pulsed column:

1. Mass transfer coefficient from liquid drop to continuous phase

2. Diameter and velocity of moving drop in the pulsed column

3. Holdup of dispersed and continuous phases in the pulsed column

4. Longitudinal dispersion coefficient in the pulsed column.

To establish the validity of the PULCO code, experiments were performed using a 50 mm diameter pulsed column which had a sieve plate section height of 2 m and plates spaced 50 mm apart. The experiments were performed by CY tests with use of unirradiated U and Pu. The experimental concentration profiles fitted well with the calculated concentration profiles.     

亚包晶钢圆坯表面纵裂及影响因素

本文从亚包晶钢的裂纹敏感性 ,表面纵裂形成及影响因素等方面进行讨论 ,初步阐述了亚包晶钢圆坯表面纵裂形成原因及各种因素对表面纵裂的影响     

改进LQR技术的飞翼式无人机控制算法研究

针对飞翼式布局无人机存在纵向操稳性能差和易受阵风干扰问题,采用一种指令跟踪增广LQR方法设计了飞翼式无人机纵向姿态控制律,该方法将系统的输出误差和外界恒值阵风干扰信号引入到性能指标函数中,使设计出来的控制器不仅能保证飞行姿态的无静差跟踪,而且能有效抑制外界的阵风干扰。考虑到系统的迎角变量不易检测,结合降维观测器得到了一种准指令跟踪增广LQR方法,该方法不仅具有良好的鲁棒性和跟踪性,而且便于工程实现。最后利用获得的控制律对ICE飞翼式无人机进行仿真实验和对比分析,结果表明,采用改进后的LQR方法设计的控制器不仅改善了飞翼式无人机纵向模态的飞行品质,同时与输出反馈线性二次型跟踪方法和LQG/LTR方法相比,具有更好的控制性能。     

基于宽频激励电磁声谐振7075铝合金板厚检出概率

电磁超声换能器(EMAT)换能效率低、激发信号弱,而基于长周期激励信号以产生声波共振的电磁声谐振技术(EMAR)虽然可以提高接收信号的信噪比,然而可能导致主脉冲加宽并扩大超声波检测盲区,降低测量精度.本文应用一种宽频激励电磁声谐振技术(BE-EMAR)和一种Halbach阵列纵波EMAT,以单周期宽频激励作为EMAT输...     

钢箱梁制造横向分段和纵向分段方案的对比分析

通过钢桥钢箱梁制造中横向分段和纵向分段两种方案的比较,从制造、运输及安装架设等方面分析两种方案各自特点,结合工程实践,予以阐述。     

飞秒激光参数对硅橡胶表面结构与防冰性能影响的研究

目的 采用飞秒激光刻蚀硅橡胶表面,获得表面结构较优、润湿性能与防冰性能优异的超疏水硅橡胶表面。方法 通过控制变量,设计单因素试验,研究飞秒激光参数(填充间距、能量密度、扫描速度)对硅橡胶表面结构的影响规律。基于正交试验设计和极差分析获得使表面结构规整且表面粗糙度最大的相对最优工艺参数,研究飞秒激光参数对表面粗糙度的影响主次顺序。结果 飞秒激光刻蚀硅橡胶的相对最佳工艺参数如下:能量密度为5 J/cm²,扫描速度为200 mm/s,填充间距为20 μm。最优参数组下激光刻蚀的超疏水硅橡胶表面粗糙度达到最大值5.954 μm,具有规整的峰状凸起与微纳结构和优异的超疏水性能,水接触角高达165.3°,滚动角低至2.6°。该超疏水硅橡胶表面具有优异的防冰性能,在低温高湿环境下,与未处理的硅橡胶表面相比,结冰时间由67 s延长至312 s,冰黏附强度由39.6 kPa降低至7.4 kPa。超疏水硅橡胶还具有良好的循环除冰性能,经20次结冰/除冰循环后,冰黏附强度仍不超过20 kPa;此外,该表面还具有优异的耐腐蚀性能和良好的耐磨损性能。结论 飞秒激光增大能量密度和减小扫描速度会使激光刻蚀宽度增大,要避免纵向条纹,应控制填充间距不超过激光刻蚀宽度。激光参数优化后刻蚀出的超疏水硅橡胶表面具备优异的防冰性能,并且机械与化学稳定性较好,在恶劣环境中的防冰领域,具有广阔的应用前景。     

磁场频率对Fe5自熔合金性能的影响

在低碳钢表面进行Fe5合金等离子弧堆焊时外加纵向磁场,对堆焊试样进行磨损和硬度试验,采用显微电镜和扫描电镜对堆焊层显微组织进行分析,研究磁场频率对堆焊层金属的硬度和耐磨性的影响规律.结果表明,外加纵向磁场通过电磁搅拌作用细化堆焊层金属的组织,并控制硬质相的形态及分布;堆焊层的硬度和耐磨性随磁场的频率变化而变化并存在最佳值,在适当的磁场频率作用下电磁搅拌达到最佳效果从而提高堆焊层金属的综合力学性能.