不同孔隙率锶磷灰石陶瓷体内异位成骨能力的比较

采用健康兔的骨髓组织,体外培养,诱导分化为成骨细胞,分别与孔径约为450～700μm、孔隙率分别为50%、60%、70%的Sr-HA以及孔隙率为70%的纯羟磷灰石陶瓷体复合,自体回植到兔背脊肌内.同时以未复合细胞的相同孔隙率的陶瓷材料作为对照,植入后4周、12周和24周取材,行四环素荧光染色观察,定量计算各组陶瓷材料新骨的形成量和速度,比较不同孔隙率锶磷灰石陶瓷材料的异位成骨能力.结果表明,复合成骨细胞的各组陶瓷在植入兔背脊肌内4周后均有新骨形成,随着植入时间的延长,骨组织的数量不断增加;孔隙率为70%的Sr-HA陶瓷和HA陶瓷的新骨形成数量和速度明显优于低孔隙率的Sr-HA陶瓷.四环素荧光标记还显示未复合成骨细胞的Sr-HA陶瓷和HA陶瓷孔隙内也有荧光沉积.Sr-HA多孔陶瓷是较理想的骨组织工程支架材料,成骨细胞复合Sr-HA陶瓷用于骨缺损的修复,具有广阔的临床应用前景.     

Effect of immersion angle of a one-face sealed quartz crystal microbalance in liquid

The effect of the immersion angle theta of the QCM in a liquid was investigated using the impedance analyzer. In the QCM, with the two faces in contact with a liquid, the resonant frequency shift deltaF was independent of theta and was dependent on only the number of faces in contact with a liquid. On the other hand, in the QCM, with the one face in contact with a liquid, it became clear that deltaF depended on theta and had the largest value at theta = 90 degrees and the smallest value at theta = 0 degrees. We also presented the simple model of deltaF in the QCM with the one face in contact with a liquid on the basis of experimental results.     

Experimental pure fluid and binary mixture performance in a heat pump equipped with a distillation column

An experimental heat pump system that included a distillation column, accumulator/sump, and heater was experimentally investigated using two different working fluids, R32 and a mixture of R32/134a. Performance variations with changes in sump heater power, condenser and evaporator heat transfer fluid flow, and compressor speed were examined. Heating capacity generally increased with increases in the factors tested. Heating capacity increases were generally smaller with the R32/134a tests than with the R32 tests, except with variations in sump heater power. An increase in sump heater power caused a pronounced increase in the circulating R32 concentration during the mixture tests, and the heating capacity increased markedly. The increase in heating capacity with sump heater power during the R32/134a tests was on par with the increase with compressor power during these same tests. The increase in capacity with sump heater power during the R32/134a tests also was substantial even when compared with the capacity increase with compressor speed during the R32 tests.     

基于PD结合输入整形控制的含有刚性模态弹性机构的力及能耗分析

高速轻型机构在大幅度刚性运动的同时弹性构件存在着弹性变形,从而产生残留振动,导致刚性体运动与弹性体运动相互耦合,使整个系统难以精确定位。在研究含有刚性模态弹性机构的动力学特性的基础上,将时滞环节引入控制系统中,提出PD结合输入整形控制策略,研究在阶跃输入信号作用下PD结合输入整形控制系统的振动特性,分析输入整形对系统控制力和能耗的作用规律。在相同反馈增益的情况下,与PD反馈控制相比较,PD结合输入整形控制系统控制力降低56%,能耗降低47%,同时提高了系统的响应速度。     

Electrochemical properties of 316L stainless steel with culturing L929 fibroblasts.

Potentiodynamic polarization and impedance tests were carried out on 316L stainless steel with culturing murine fibroblast L929 cells to elucidate the corrosion behaviour of 316L steel with L929 cells and to understand the electrochemical interface between 316L steel and cells, respectively. Potential step test was carried out on 316L steel with type I collagen coating and culturing L929 cells to compare the effects of collagen and L929 cells. The open-circuit potential of 316L steel slightly shifted in a negative manner and passive current density increased with cells, indicating a decrease in the protective ability of passive oxide film. The pitting potential decreased with cells, indicating a decrease in the pitting corrosion resistance. In addition, a decrease in diffusivity at the interface was indicated from the decrease in the cathodic current density and the increase in the diffusion resistance parameter in the impedance test. The anodic peak current in the potential step test decreased with cells and collagen. Consequently, the corrosion resistance of 316L steel decreases with L929 cells. In addition, collagen coating would provide an environment for anodic reaction similar to that with culturing cells.     

Studies on elemental tellurium under high pressure

A non-linear behaviour in the resistance of tellurium as a function of pressure has been observed. At each pressure the resistance shows a time variation. At lower pressures, the normalized resistance increases with time, and at higher pressures, the normalized resistance decreases exponentially as a function of time. This change in behaviour with respect to time occurs in the region of the steepest descent in the resistance versus pressure plot. However, the magnitude of the change in the resistance with time is small compared to a change in the resistance with pressure. The origin of this behaviour is suggested to be linked with the generation and annealing of localized charged defects. This revised version was published online in November 2006 with corrections to the Cover Date.     

Comparing the pozzolanic behavior of sugar cane bagasse ash to amorphous and crystalline SiO2

The present paper aims to clarify the pozzolanic behavior of sugar cane bagasse ash-SCBA by comparing it to amorphous and crystalline silica. It is shown that calcium silicate hydrate is formed in lime solution with SCBA but the reaction is slow and does not consume all the material. Comparing its results with the obtained in tests with silica fume and with crushed quartz show a better agreement with the latter. Characterization of cement pastes shows 20% of cement replacement by sugar cane bagasse ash leads to only a minor reduction in the amount of calcium hydroxide formed. This behavior is also closer to the observed in quartz than in silica fume. The results suggest SCBA should be used as a replacement for inert constituents in cement composites rather than pozzolanic addition. Analysis of the microstructure of the cement pastes revealed the presence of calcium hydroxide in samples prepared with partial replacement by silica fume, quartz and sugar cane bagasse ash. The presence of this phase in the sample prepared with silica fume was attributed to agglomeration of the particles that affected the reactivity of this material.     

Horacio Coppola: Towards an Aesthetic Genealogy

Although a milestone in the history of Latin American photography, the work of Horacio Coppola is little known outside Argentina. His unorthodox angles and tilting frames, his attention to industrial and urban themes, and his experimentation with different lenses in the period between 1927 and 1931 were in absolute synchrony with the precepts of European New Vision and New Objectivity photography, and with American straight photography. That Coppola’s visual idiom was in tune with the latest photographic developments in interwar Europe is obvious. What remains unclear is how exactly he achieved that synchrony. Several scholars have wrestled with this question, which nevertheless remains elusive due to lack of evidence of direct contact with European photography prior to his studies at the Berlin Bauhaus in 1932 and his repeated attempts to downplay the influence contemporary photographers had on his work. The article provides a systematic study of Coppola’s aesthetic genealogy and his photographic borrowings through a critical examination of his early pictures and theoretical writings. It teases out possible direct and indirect channels of dialogue with the New Vision, New Objectivity, and straight photography in the second half of the 1920s, and probes the reasons behind Coppola’s reluctance to admit a connection with contemporary European photography in particular.     

Infrared study of the interaction of dental polycarboxylate cements with tooth structure and some metals

The interaction of three commercial zinc polycarboxylate cements with tooth structure was investigated by using infrared spectroscopic techniques. The obtained data revealed that the cements interact with enamel and ionic bonds are formed between calcium ions in enamel and carboxyl groups in polycarboxylic acid. The interaction depends on the percentages of ZnO content in the powders and of carboxylic acid in the liquids of these cements. The results provided some evidence that the cements also may interact with dentin but to a lesser extent than with enamel. The interaction of the cements with the metals copper and nickel or with Cr₂O₃, was also studied.     

基于近场动力学微分算子的变截面梁动力特性分析方法EI北大核心CSCD

变截面梁式构件广泛应用于工程结构中,其动力特性更是结构设计和状态评估中的重要考虑因素之一。基于新兴的近场动力学微分算子(Peridynamic differential operator,PDDO),尝试提出了一种用于变截面梁动力特性分析的非局部方法。将变截面梁的动力学微分控制方程与边界条件通过PDDO由局部微分形式转化为对应的非局部积分形式,再结合拉格朗日乘数法与变分原理,将非局部积分形式的控制方程与边界条件转化为标准特征值问题表达形式,从而求得自振频率与振型。通过对等截面梁的自由振动分析并与解析解对比,验证了该方法良好的收敛性与准确性。进一步通过求解下边界一次、二次变化的连续变截面梁,证明了该方法对于任意变截面梁自由振动分析的适用性与可靠性。开展含孔变截面梁的自由振动分析,体现了该文的非局部方法在含缺陷构件振动分析和损伤识别问题方面的潜力,可为含缺陷变截面构件的动力分析问题提供新思路。     

A study on bullock carts. Part 2. Experimental study of forces in a bullock cart

A strain gauge load cell with separate bridges for measurement of the pull and the bending moment in the plane containing the net neck load and pull was developed and fixed in the longitudinal member of an experimental cart. A cart fitted first with pneumatic wheels and then with steel-rimmed wooden wheels was tested on three terrains—tar road, mud road and grassy terrain. Pull vs time and moment vs time records were obtained in each test and analysed. It is found that the bullocks pull the cart rather discontinuously at the low velocities at which these carts normally operate. On the tar road and the grassy terrain, the mean static coefficient of friction is significantly higher for the cart with steelrimmed wooden wheels. The dynamic frictional resistance of the terrain for the cart with steel-rimmed wooden wheels is lower than for the cart with pneumatic wheels so long as the wheels do not dig or sink into the terrain. The fluctuation in the neck load is lower in the cart fitted with pneumatic wheels. Also, the ground-induced low-amplitude high-frequency vibratory load content in the neck load is lower in the cart with pneumatic wheels.     

Influence of different types of water on strength, porosity and hydric parameters of metakaolin admixtured cement

The present research deals with strength, porosity and hydric behavior of metakaolin cement admixtured with different types of water. The hydration of ordinary Portland cement in the presence of 0%, 10%, 20% and 30% metakaolin treated with distilled, ground and sea water with the water to cement ratio of 0.4 was studied. The experimental results on setting time, strength, porosity and hydric parameters are reported. The results show that, metakaolin percentage increases in strength with a decrease in porosity. The observed results are discussed with SEM micrographs. Further, sea water accelerates the cement hydration at the early stages but retards it in the latter stages of hydration.     

In vitro conditions for the study of the in vivo performance of sustained-release theophylline matrix tablets administered in fasted conditions and with a high-fat diet

Dissolution profiles of theophylline (TP) from three types of sustained-release (SR) matrix tablets (plastic [PL], lipid [LP], and hydrophilic [HP]) in different dissolution media, with and without enzymes, were established. Also investigated was the influence of a treatment of the tablets with peanut oil prior to the dissolution test. The in vivo behavior of the tablets under the fasted state and with the concomitant administration with a high-fat diet was previously evaluated; the diet produced changes in the absorption profiles for the three matrix tablets in comparison with fasted administration. Level A correlations were obtained between cumulative percentage dissolved (CPD) and cumulative percentage absorbed (CPA). For the fasted condition, better correlations were obtained with water as the dissolution medium for the HP and LP matrix; for PL matrix, the best correlation was obtained with a medium with gradual change of pH. The pretreatment with peanut oil showed better correlations for the fed state.     

The effect of martensite volume fraction and particle size on the tensile properties of a surface-carburized AISI 8620 steel with a dual-phase core microstructure

This study is focused on the production of a dual-phase steel structure in the core of a surface-carburized AISI 8620 cementation steel and the effect of martensite volume fraction (MVF) and martensite particle size (MPS) on tensile properties. Experimental results showed that, compared with specimens with a fully martensitic microstructure in the core, those with a dual-phase microstructure in the core exhibited slightly lower tensile and yield strength but superior ductility without sacrificing surface hardness. In specimens with a dual-phase microstructure in the core, the tensile strength increased and ductility decreased with increasing MVF. Both the tensile strength and the ductility increased with decreasing MPS at constant MVF. The best combination of tensile strength and ductility was obtained with a fine MPS at a constant MVF of 25%.     

Fatality risk in motorcycle collisions with roadside objects in the United States

Motorcycle crashes with roadside objects often involve more than one impact event: typically involving a collision with the ground and another object. The objective of this study was to determine the fatality risk in these roadside object collisions when compared with crashes only involving a collision with the ground. The roadside objects analyzed included guardrails, concrete barriers, signs, utility poles, and trees. The Fatality Analysis Reporting System (FARS) database was used in conjunction with the General Estimates System (GES) to analyze fatality risk for motorcycle crashes from 2004 to 2008. The analysis was based upon over 3600 fatal motorcycle crashes with roadside objects. Collisions with roadside objects were found to have a higher fatality risk than collisions with either the ground or another motor vehicle. Based on the most harmful event reported in the crash, motorcycle collisions with guardrail were 7 times more likely to be fatal than collisions with the ground, and collisions with trees were almost 15 times more likely to be fatal than collisions with the ground. Additionally, the roadside object was reported as the most harmful event in the majority of the crashes in fatal two-event crashes involving a roadside object and a collision with the ground, with the exception of collisions with signage. From these analyses it was concluded that collisions with fixed objects are more harmful to motorcyclists than collisions with the ground.     

Determinants of success for biomedical researchers: a perception-based study in a health science research environment

New institutions are coming to the fore as stakeholders in research, particularly hospitals and clinical departments involved in providing health care. As a result, new environments for research are gaining importance. This study aims to investigate how different individual characteristics, together with collective and contextual factors, affect the activity and performance of researchers in the particular setting of hospitals and research centres affiliated with the Spanish National Health System (NHS). We used a combination of quantitative science indicators and perception-based data obtained through a survey of researchers working at NHS hospitals and research centres. Inbreeding and involvement in clinical research is the combination of factors with the greatest influence on scientific productivity, because these factors are associated with increased scientific output both overall as well as in high-impact journals. Ultimately, however, satisfaction with human resources in research group combined with gender (linked in turn to leadership) is the combination of factors associated most clearly with the most relevant indicator of productivity success, i.e. the number of articles in high-impact journals as principal author. Researchers’ competitiveness in obtaining research funding as principal investigator is associated with a combination of satisfaction with research autonomy and involvement in clinical research. Researchers’ success is not significantly related with their age, seniority and international experience. The way health care institutions manage and combine the factors likely to influence research may be critical for the development and maintenance of research-conducive environments, and ultimately for the success of research carried out in hospitals and other settings within the national public health system.     

A transmission electron microscopy study of WC-10Co cemented carbides with modified hard and binder phases

The alloy design of WC-10Co cemented carbide, modified with addition of a hard carbide phase, TiC, and with Ni and Mo in the binder phase, has been highlighted by the authors in a number of publications. The present article deals with the fine microstructural features of various phases in such cemented carbides. WC grains in all the investigated cemented carbide compositions appear to develop straight facets during sintering because of their anisotropic nature. In contrast, the TiC phase is characterized by its rounded shape. Dislocations are present in both WC and TiC grains, being of lesser density in the latter. The binder phase is always associated with stacking faults. The nature of the hard phase/binder interfaces has been found to be dependent on the binder phase chemistry. The observed changes in microstructures and mechanical properties have been correlated with the wettability and solubility of the hard phases in the binder melt, and with the different strengthening mechanisms in the binder phase.     

高分辨率CT(HRCT)扫描技术在鼻骨骨折诊断中的应用价值

目的：探讨高分辨率CT(HRCT)扫描技术在鼻骨骨折诊断中的应用价值。材料与方法：对32例鼻骨骨折患者的CT资料进行回顾性分析。32例鼻骨骨折患者均行轴位加冠状位HRCT扫描。结果：19例鼻骨粉碎性骨折，13例线性骨折。合并上颌骨额突骨折8例，额骨骨折4例，眼眶壁骨折10例，鼻中隔骨折2例，鼻额缝分离2例。结论：HRCT扫描技术对鼻骨骨折的诊断有较高临床应用价值，轴位扫描和冠状位扫描相结合的HRCT扫描可作为鼻骨骨折常规和首选的检查方法。     

杭氧空分设备精馏塔的技术现状及进展

阐述了杭氧空分设备精馏塔的技术现状,介绍了大型高效筛板塔及高效规整填料塔的开发历程、应用及其最近的研究进展;谈了一些技术发展中的体会,并找出与先进水平的差距及技术发展中的不足,提出了今后空分设备精馏塔技术的研究方向     

采用不同膨胀机构的跨临界CO2循环性能分析

运用热力学第一定律和第二定律对跨临界CO2基本循环、膨胀机循环、喷射器循环和涡流管循环进行了分析,计算了各循环各个部件的损失,比较了各循环性能系数和总损失。计算结果表明,采用膨胀机、喷射器和涡流管等膨胀设备代替基本循环中的节流阀后,由于这些改进膨胀设备的损失小于基本循环节流阀的损失,同时改进循环中压缩机的损失小于基本循环的压缩机损失,从而减小了循环总损失,提高了循环的COP。膨胀机循环的COP远大于其它跨临界CO2循环,其次为喷射器循环和涡流管循环。