Poly(para‐dioxanone) and poly(L‐lactic acid) blends: thermal,mechanical, and morphological properties

Blends of two semicrystalline polymers, poly(L ‐lactic acid) (PLLA) and poly‐p‐dioxanone (PPD) have been prepared by solvent casting in different compositions. Thermal, morphological, and mechanical properties of the blends were studied using modulated differential scanning calorimetry, wide‐angle X‐ray diffractometry, scanning electron microscopy (SEM), polarizing light microscopy (PLM), and tensile tests. Thermal analysis showed two glass transition temperatures nearly constant and equal to the values of the homopolymers and constant values of melting temperature (T_m) for all blend compositions, suggesting that both polymers are immiscible. The PLM and SEM observations validated these results, and showed the different morphology obtained by changing the composition of the blend. The blends 40/60, 50/50, and 60/40 presented a clearly macroseparated system, while the 20/80 and 80/20 blends presented better homogeneity, probably due to the low amount of one component in the other. It was found by PLM that PPD is able to crystallize according to a spherulitic morphology when its content is above 40%. Under this content, the crystallization of PPD is hardly observed. The blend 20/80 is more flexible, and tough material and neck formation during elongation is also observed, due to PPD, which may act as a plasticizer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 12: 2744–2755, 2003     

水热沉积电压对C-AlPO_4涂层显微结构的影响

以方石英型磷酸铝(C-A1PO4)粉体为原料,异丙醇为溶剂,碘为荷电介质,采用水热电泳沉积方法在涂有SiC涂层的碳纤维增强碳(C/C-SiC复合材料表面制备了C-A1PO4外涂层.借助X射线衍射和扫描电镜表征了涂层的晶相组成和显微结构.研究了沉积电压对C-A1PO4涂层显微结构的影响,并测试了涂层的抗氧化性能.结果表明:在180～220V范围内,水热沉积电压对涂层的显微结构有较大的影响,220V时制备的涂层致密均匀.涂层的沉积量以及涂层与基体的结合强度随着沉积电压的升高而增加;单位面积沉积量与时间的二次方根之间符合线性关系.与包埋法制备的SiC涂层相比,水热电泳沉积法制备的C-A1PO4涂层具有更好的抗氧化性能,涂层样品在1500℃的空气中氧化37h后质量损失仅为0.53%.     

注射成型中浇口形式对塑件质量的影响

用生产实例介绍了不同浇口形式及位置对塑料熔体在型腔中的填充模式和注射成型后塑件的内在机械物理性能及表观质量的影响。     

热交换器在线清洗实施方案研究

热交换器的污垢问题是国民经济众多产业和部门急需解决的问题,也是传热学界未彻底解决的主要问题之一。在分析热交换器污垢的主要成分及形成机理的基础上,针对污垢成分配制了相应的清洗配方,设计了清洗流程及装置,得到了完整可行的热交换器在线清洗实施方案。     

旋转导向钻井系统中振动加速度的消除方法

在钻井过程中,钻头切削岩层、钻柱与井壁的碰撞,必然造成钻井工具的振动,这些振动会在测斜加速度传感器的输出上得到反映,使其不能真实地反映井眼姿态的变化。为及时得到准确的井眼姿态,有必要研究振动条件下传感器的输出规律,进而消除振动的影响。从室内模拟振动实验的原始数据入手,通过Matlab对传感器输出信号进行功率谱密度估计,得出了振动频率与转速的大致关系,并设计了具有针对性的滤波器。通过对实验数据分析处理,振动干扰信号的能量得到大幅衰减,测斜传感器3个敏感轴的输出波动明显减小,提高了姿态测量的准确性,从而验证了该方法在旋转导向系统中是可行的。     

开放式数控系统实验教学平台研究

针对目前机电一体化专业机电综合性实验相对薄弱的问题,构建基于PMAC运动控制器的开放式数控实验教学平台.在此基础上进行伺服随动控制、控制系统校正环节设计、机电系统控制性能分析等实验教学工作,加深了数控实验教学内容,改善了机电综合实验和相关课程的教学效果.     

Selective iodine imaging using K-edge energies in computerized x-ray tomography

Iodine is commonly used as a contrast material in computerized x-ray tomography. In some cases the determination of the iodine distribution in the image may be prevented by the presence of bone or tissue variations within the tomographic slice. This paper describes a method for quantitative selective imaging of the iodine concentration in the slice. The method employs scans using three heavily filtered x-ray beams, two having mean energies which straddle the iodine K edge (33 keV) and another at a slightly higher energy. The results are independent of tissue and bone over a broad range of projection path lengths. It is shown that, for separation of iodine from one other material, a two-beam K-edge approach requires less integral dose than a two-beam technique at conventional CT energies for slice diameters up to 30 cm. For selective iodine imaging in the presence of more than one other material, the three-spectrum K-edge technique is a necessity. Exposure requirements and beam-hardening corrections are discussed in detail and a computer-simulated CT image generated by the proposed scheme is presented.     

Correlation of cerebral blood flow with outcome in head injured patients

In order to determine the relationship of cerebral blood flow (CBF) to the clinical outcome of head injury, serial determinations of CBF were performed by the intravenous Xenon technique in 24 patients. The patients were of mixed injury severity and were classified into four groups depending on the neurological exam at the time of each CBF study. All eight patients who were lethargic on admission demonstrated increases in their minimally depressed CBF as they improved to normal status. Eleven patients in deep stupor or coma ultimately recovered. Ten of these patients initially had moderate to profound decreases in CBF which improved as recovery occurred. The single exception was an adolescent whose initial CBF was high but became normal at recovery. Five comatose patients died. In four of these, already depressed CBF fell even lower, while one adolescent with initially increased CBF developed very low CBF preterminally. The data presented in this report demonstrated a good correlation between CBF and clinical outcome. In every one of the adult survivors, depressed CBF increased as the patient recovered to normal status. All adults who died showed a deterioration of CBF as the neurological status worsened. The only exceptions were two adolescents who initially showed high CBF values. In the adolescent who died, CBF dropped to low levels while in the survivor a normal CBF was achieved. Thus in adults a traumatic brain injury was associated with depressed CBF which increased with recovery or decreased further with deterioration while the reaction to injury was quite different in the younger brain.     

Influence of the number of questions on the student''s achievement in tests of anatomy

The authors compare student's achievement in tests with low and moderately high number of questions requiring short answers. Five groups of Medical School students underwent their regular Anatomy evaluation tests, which consisted of 13 questions (one group), 15 (two groups) and 25 (two groups). In each group five questions were chosen at random, average scores being calculated from their marks. These scores were statistically compared to the ones calculated from the marks given to the full-length evaluation tests; it became quite evidente that averages go up when the number of questions is increased. Putting the averages in terms of A, B, C and D scores (very good, good, regular and insufficient), it was noted that failure to reach at least the C score is inversely proportional to the number of questions. The results are discussed in terms of determining the most proper number of questions to be given in a test.