Characterisation of pendular capillary bridges derived from experimental data using inverse problem method

In this study we use the recent analytical model to analyze capillary interactions in liquid bridge between two spherical grains, with fixed volumes of liquid and varying separation distance. Sequences of images of capillary bridges with different parameters are recorded during experimental tests. Geometrical parameters, as contact angle, half-filling angle and neck radius, are determined by image processing. Profiles of examined bridges are approximated as a Delaunay’s roulette and superposed on recorded images. Evolution of associated variables (Laplace pressure, capillary force) is also calculated. Results of theoretical modeling are compared with the experimental ones. They match very accurately for small volumes and/or small separation distances, when influence of gravity is not significant. For larger liquid volumes and/or larger separation distances between grains the influence of the gravity is observed as a distortion (loss of symmetry) of capillary bridge. To avoid this deformation, several test were realized in micro-gravity conditions. For these tests, theoretical results are in good agreement with experimental ones, also for higher liquid volumes and/or separations distances.     

Evaporation-induced evolution of the capillary force between two grains

The evolution of capillary forces during evaporation and the corresponding changes in the geometrical characteristics of liquid (water) bridges between two glass spheres with constant separation are examined experimentally. For comparison, the liquid bridges were also tested for mechanical extension (at constant volume). The obtained results reveal substantial differences between the evolution of capillary force due to evaporation and the evolution due to extension of the liquid bridges. During both evaporation and extension, the change of interparticle capillary forces consists in a force decrease to zero either gradually or via rupture of the bridge. At small separations between the grains (short & wide bridges) during evaporation and at large volumes during extension, there is a slight initial increase of force. During evaporation, the capillary force decreases slowly at the beginning of the process and quickly at the end of the process; during extension, the capillary force decreases quickly at the beginning and slowly at the end of the process. Rupture during evaporation of the bridges occurs most abruptly for bridges with wider separations (tall and thin), sometimes occurring after only 25 % of the water volume was evaporated. The evolution (pinning/depinning) of two geometrical characteristics of the bridge, the diameter of the three-phase contact line and the “apparent” contact angle at the solid/liquid/gas interface, seem to control the capillary force evolution. The findings are of relevance to the mechanics of unsaturated granular media in the final phase of drying.     

Pedestrian self-reports of factors influencing the use of pedestrian bridges

The study was designed to find out factors that influence use/non-use of pedestrian bridges. The use rate of five pedestrian bridges was observed in the central business district (CBD) of Ankara. After the observations, a survey was conducted among pedestrians using those bridges and crossing contrary to safe practice under them at street level (n=408). In the present data, the use rate of pedestrian bridges varied from 6 to 63%. The frequent use of the bridge when crossing the road concerned, and seeing bridge use as time saving and safe in general were positively related to respondents' bridge use. Frequent visits to CBD decreased the likelihood of using the bridge. Other factors accounted only for a small proportion of variance in bridge use. The study suggests that bridge use or non-use is a habit and not coincidental behaviour. For increasing the pedestrians' bridge use, escalators seem to be a good solution, but traffic signals under a bridge may deteriorate the use rate. In addition, increasing the number of legs leading to the bridge may not increase the use rate. The use rate is likely to improve, if the safety benefits and convenience of using the bridge without considerable time loss are clearly visible to pedestrians.     

意大利高速铁路Sesia大桥的动力特性及车桥耦合振动分析

建立了包括钢轨、轨枕、道床、梁体在内的意大利Sesia大桥空间有限元模型,对桥梁的自振特性进行了计算和实测分析。按照轮轨密贴接触假定推导了车-桥系统耦合运动方程组,以德国低干扰谱生成轨道不平顺样本作为激励源,对意大利ETR500Y高速列车通过Sesia大桥引起的桥梁动力响应和桥上车辆的振动响应进行了计算分析,讨论了共振车速的范围并对桥上车辆的运行安全性和平稳性进行了评价。部分计算结果与实测数据进行了对比,吻合较好,从而验证了所建立的模型及分析方法的精度和有效性。结果表明：Sesia大桥结构刚度很大,当列车以288km/h的速度通过时,挠跨比只有1/17510;当列车以340km/h的速度通过时,桥梁的竖向位移出现了一个较为明显的峰值,说明这一速度可能引发结构共振;桥上车辆的各项动力指标响应值均很小,能较好地满足高速行车要求。     

One-step concentration of analytes based on dynamic change in pH in capillary zone electrophoresis

A novel strategy for one-step concentration of analytes during capillary electrophoresis (CE) is presented. A short platinum wire was inserted into the 75-microm-i.d. separation capillary. When a high voltage was applied for CE separation, a sharp pH gradient along the capillary was created dynamically by the electrolysis of water in the running buffer. Concentration of a large volume of injected analytes was accomplished by the change in analyte charge due to the dynamic pH gradient. Depending on the polarity of the applied potential and the direction of electroosmotic flow, either anions or cations can be concentrated. Several hundredfold concentration factors were achieved. Fluorescence imaging by a CCD camera was used to monitor 10 cm of the capillary near the platinum wire during the concentration process. The observations are consistent with a sweeping mechanism.     

桥墩不均匀沉降对高速列车运行安全影响研究

针对运营阶段列车循环加载导致软土地基桥梁产生附加不均匀沉降威胁行车安全性问题,分别建立车辆-桥梁动力相互作用模型、桩基础-地基沉降模型。将用动力模型获得列车过桥时支反力时程作为外部激励,利用沉降模型研究列车荷载作用下桩基础的累积沉降规律;将由桥墩沉降产生的附加线形变化叠加到原始轨道不平顺中,考虑由其引起的竖向类离心力影响,用动力模型研究桥墩不均匀沉降对列车行车安全影响。以德国ICE3高速列车及三跨32 m简支梁桥为研究对象进行实例分析,结果表明,软土累积沉降主要发生在桩底约10 m厚土层范围内;相邻桥墩沉降引起的桥梁相对上拱对行车安全更不利。     

Monitoring the electroosmotic flow in capillary electrophoresis using contactless conductivity detection and thermal marks

The fundamental aspects and the capillary electrophoresis usage of thermal marks are presented. The so-called thermal mark is a perturbation of the electrolyte concentration generated by a punctual heating of the capillary while the separation electric field is maintained. The heating pulse is obtained by powering tungsten filaments or surface mount device resistors with 5 V during a few tens to hundreds of milliseconds. In the proposed model, the variation of the transport numbers with the rising temperature leads to the formation of low- and high-concentration regions during the heating. After cooling down, the initial mobilities of the species are restored and these regions (the thermal mark) migrate chiefly due to the electroosmotic flow (EOF). The mark may be recorded with a conductivity detector as part of a usual electropherogram and be used to index the analyte peaks and thus compensate for variations of the EOF. In a favorable case, 10 mmol/L KCl solution, the theory suggests that the error in the measurement of EOF mobility by this mean is only -6.5 x 10(-7) cm2 V-1 s-1. The method was applied to the analysis of alkaline ions in egg white, and the relative standard deviations of the corrected mobilities of these ions were smaller than 1%. This is a challenging matrix, because albumin reduces the EOF to 20% of its initial value after 11 runs. The combination of thermal mark, electrolysis separated, and contactless conductivity detection allowed the measurement of the EOF of a silica capillary with unbuffered KCl solution with constant ionic strength. The overall approach is advantageous, because one can easily control the chemical composition of the solution in contact with the inner surface of the capillary.     

A chip-based electrophoresis system with electrochemical detection and hydrodynamic injection

A simple capillary electrophoresis system in the planar format that uses a new, hydrodynamic injection principle is described. The system was realized with poly(dimethylsiloxane)-glass chips and microdisk electrodes for amperometric detection. Using a double-tee injector, no precise voltage control of the electrolyte reservoirs was needed, thus making the microchip CE system more user-friendly. The analytical characteristics of chip-based CE-EC were evaluated using ascorbic acid as the model analyte. The reproducibility of migration time and signal height was expressed by relative standard deviations of 1.2% and 5.1%, respectively (n = 5). The limit of detection for ascorbic acid was approximately 5 microM at a signal-to-noise ratio of 3. Practical application concerning the determination of physiologically relevant compounds such as noradrenaline and L-dopa are discussed.     

Combinatorial synthesis of highly selective cyclohexapeptides for separation of amino Acid enantiomers by capillary electrophoresis

Cyclic peptide libraries dissolved in the electrolyte solution can be used as chiral selectors in capillary electrophoresis. In the present investigation, the resolution obtained in capillary electrophoresis for a set of dinitrophenyl-d,l-amino acids was the parameter used to screen for the most effective selectors contained in a mixture of thousands of components of a cyclic hexapeptide sublibrary with three randomized positions. The deconvolution procedure was simplified by fractionating the sublibrary components according to the hydrophobicity of the amino acids in the randomized positions through reversed-phase HPLC. By comparing the resolution obtained with the separated fractions, a set of hydrophobic amino acids was recognized as essential to achieve adequate enantioselectivity. The whole deconvolution process, which made it possible to select two highly selective cyclopeptides, required the synthesis and the evaluation of 15 sublibraries instead of the 54 syntheses required by a classical procedure of serial deconvolution.     

Enhancement of Separation Efficiency in Capillary Electrophoresis by Electrostacking without Liquid Contact

Quantitative reproducibility and separation efficiency in high-performance capillary electrophoresis is often limited by the reproducibility and the nature of the sample introduction procedure. This is particularly true where electrostacking is involved, whether such is deliberately carried out or happens automatically with the choice of ionic strength of the running electrolyte. Extraneous dispersion frequently originates in the act of sample introduction, for example, from the shock of the capillary entering a sample vial or a sample-filled capillary entering the carrier electrolyte source vial. A method based on the stacking of the sample constituents, before the capillary actually contacts the liquid in a vial, can reduce this problem. This technique can be utilized for the preconcentration of sample constituents and to improve separation efficiency by reducing dispersion. In favorable cases, plate counts can increase by as much as 160%, approaching theoretical diffusion-limited efficiencies.     

Bubble-free operation of a microfluidic free-flow electrophoresis chip with integrated Pt electrodes

In order to ensure a stable and efficient separation in microfluidic free-flow electrophoresis (FFE) devices, various methods and chips have been presented until now. A major concern hereby is the generation of gas bubbles caused by electrolysis and the resulting disturbances in the position of the separated analyte lanes. Instable lane positions would lead to a decreased resolution in sample collection over time which certainly would be problematic when incorporating a stationary detector system. In contrast to our previous publications, in which we implemented laborious semipermeable membranes to keep bubbles outside the separation region, here we describe an electrochemical approach to suppress the electrolysis of water molecules and therefore bubble formation. This approach allowed a simpler and additionally a closed chip device with integrated platinum electrodes. With the use of this chip, the successful separation of three fluorescent compounds was demonstrated. Quinhydrone, which is a complex of hydroquinone and p-benzoquinone, was added only to the local flow streams along the electrodes, preventing mixing with the separation media and sample. The electrical current was generated via the oxidization and reduction of hydroquinone and p-benzoquinone up to a certain limit of the electrical current without gas formation. The separation stability was investigated for the chip with and without quinhydrone, and the results clearly indicated the improvement. In contrast to the device operating without quinhydrone, a 2.5-fold increase in resolution was achieved. Furthermore, separation was demonstrated within tens of milliseconds. This chemical approach with its high miniaturization possibilities offers an interesting alternative, in particular for low-current miniaturized FFE systems, in which large and open electrode reservoirs are not tolerable.     

Nonaqueous capillary zone electrophoresis of synthetic organic polypeptides

Poly(Nepsilon-trifluoroacetyl-L-lysine) was used as a model solute to investigate the potential of nonaqueous capillary electrophoresis (NACE) for the characterization of synthetic organic polymers. The information obtained by NACE was compared to that derived from size exclusion chromatography (SEC) experiments, and the two techniques were found to be complimentary for polymer characterization. On one hand, NACE permitted (i) the separation of oligomers according to their molar mass and (ii) the separation of the polymers according to the nature of the end groups. On the other hand, SEC experiments were used for the characterization of the molar mass distribution for higher molar masses. Due to the tendency of the solutes (polypeptides) to adsorb onto the fused-silica capillary wall, careful attention was paid to the rinsing procedure of the capillary between runs in order to keep the capillary surface clean. For that purpose, the use of electrophoretic desorption under denaturating conditions was very effective. Optimization of the separation was performed by studying (i) the influence of the proportion of methanol in a methanoVacetonitrile mixture and (ii) the influence of acetic acid concentration in the background electrolyte. Highly resolved separation of the oligomers (up to a degree of polymerization n of approximately 50) was obtained by adding trifluoroacetic acid to the electrolyte. Important information concerning the polymer conformations could be obtained from the mobility data. Two different plots relating the effective mobility data to the degree of polymerization were proposed for monitoring the changes in polymer conformations as a function of the number of monomers.     

High-resolution capillary isoelectric focusing-electrospray ionization mass spectrometry for hemoglobin variants analysis

On-line capillary isoelectric focusing (CIEF)-electrospray ionization mass spectrometry (ESIMS) as a two-dimensional separation system is employed for high-resolution analysis of hemoglobin variants A, C, S, and F. The effects of moving ionic boundary inside the CIEF capillary and MS scan rate on the separation resolution and mass detection of hemoglobin variants are investigated. The formation of a moving ionic boundary due to the replacement of background electrolyte counterions with sheath liquid counterions can be minimized by combining cathodic mobilization with a gravity-induced hydrodynamic flow. Hemoglobin variants F and A, with a pI difference of 0.05 pH unit, are almost baseline resolved and identified in CIEF-ESIMS. The concentration detection limit for each hemoglobin variant is in the range of 10(-)(8) M, comparable to that obtained in two-dimensional gel electrophoresis using silver staining. Initial preconcentration during the focusing step and the use of single-ion monitoring scan mode are responsible for improving detection limits.     

Developments and Prospects of Long-Span High-Speed Railway Bridge Technologies in China

With the rapid developments of the high-speed railway in China, a great number of long-span bridges have been constructed in order to cross rivers and gorges. At present, the longest main span of a constructed high-speed railway bridge is only 630 m. The main span of Hutong Yangtze River Bridge and of Wufengshan Yangtze River Bridge, which are under construction, will be much longer, at 1092 m each. In order to overcome the technical issues that originate from the extremely large dead loading and the relatively small structural stiffness of long-span high-speed railway bridges, many new technologies in bridge construction, design, materials, and so forth have been developed. This paper carefully reviews progress in the construction technologies of multi-function combined bridges in China, including combined highway and railway bridges and multi-track railway bridges. Innovations and practices regarding new types of bridge and composite bridge structures, such as bridges with three cable planes and three main trusses, inclined main trusses, slab-truss composite sections, and steel-concrete composite sections, are introduced. In addition, investigations into high-performance materials and integral fabrication and erection techniques for long-span railway bridges are summarized. At the end of the paper, prospects for the future development of long-span high-speed railway bridges are provided.     

撞击荷载作用下高速铁路桥梁的动力响应及列车运行安全分析

建立了“列车-桥梁-撞击荷载”系统动力分析模型,通过在松花江大桥进行的现场试验,得到了流冰撞击力时程,施加到桥墩上作为系统的激励。编制了分析程序,以高速铁路5×32m预应力混凝土简支单线箱梁桥为算例,通过计算机模拟,对流冰撞击作用下桥梁结构的动力响应及桥上高速列车的运行安全问题进行了研究。分析了在有流冰、无流冰撞击作用两种情况下,桥梁结构关键部位的位移和加速度响应,以及桥上高速运行列车的车辆脱轨系数和轮重减载率等行车安全指标。计算结果表明:流冰撞击作用对桥梁结构以及高速列车的动力特性具有较大的影响,撞击作用使桥梁和车辆的动力响应大幅度增大。当流冰撞击荷载峰值达到4000kN时,车辆减载率已经超过了0.6的限值。撞击荷载作为一项特殊的作用力,在高速铁路桥梁的动力设计中应予以重视。     

六线双层铁路钢桁桥车桥系统气动特性风洞试验研究

为研究多线双层铁路桥梁车辆与桥梁的气动特性,利用三分力分离装置-交叉滑槽系统,对某六线双层大跨铁路斜拉桥进行节段模型风洞试验。测试了不同车桥组合下车辆与桥梁各自的气动力,研究了单列车的位置、双车同层交会、双车上下层共存时车辆和桥梁气动特性的相互影响,并讨论了风攻角对上层车辆气动力的影响。试验结果表明,当车辆位于桥梁断面不同位置时,车辆气动力差异较大;由于上层桥面宽度较大,气流经过桥梁断面前缘分离后,再附着于较靠后的背风侧车辆,导致背风侧车辆的阻力系数更大;双层车辆共存时,当两者同处于迎风侧,气动力有明显的相互影响;风攻角对背风侧车辆的气动力影响显著。     

一种基于桥梁变形后构形的车辆—柔性桥梁竖向耦合模型

基于车—桥振动桥梁变形后的构形,建立了考虑桥梁变形的车—桥耦合模型。类似于结构抗震分析中,将地震作用下结构的动位移分解为拟静力位移和结构动位移,本文将车辆的运动分解为整体顺着桥面运行和相对自身局部系统的振动。以单轴车辆—简支梁桥为例,建立了基于桥梁变形后构形的车—桥系统竖向振动方程。最后,通过简支梁数值算例对由于桥梁变形产生的附加力进行了分析和研究。     

Characterization of Nonbonded Poly(ethylene oxide) Coating for Capillary Electrophoresis via Continuous Monitoring of Electroosmotic Flow

We examined changes in a poly(ethylene oxide) (PEO) coating by continuously monitoring the electroosmotic flow (EOF) in a fused-silica capillary during electrophoresis. An imaging CCD camera was used to follow the motion of a fluorescent neutral marker zone along the length of the capillary. The PEO coating was shown to reduce the velocity of EOF by more than 1 order of magnitude compared to a bare capillary at pH 7.0. However, it did not reduce EOF efficiently at pH 8.2. The coating protocol was important, especially at an intermediate pH of 7.7. Capillary reconditioning with an acidified solution of PEO was necessary in order to create a stable and efficient coating. In all cases we observed a gradual increase of EOF during extended runs, suggesting that the coating is slowly being degraded. The increase of pH in the cathodic (detection-end) buffer reservoir beyond pH ～8.0, e.g., as a result of electrolysis, had a large impact on the stability of the coating. This phenomenon may be used for the efficient and fast regeneration of the column surface and provides a simpler and more reliable alternative to pressure flushing of the capillary.     

Automated instrumentation for comprehensive isotachophoresis-capillary zone electrophoresis

An automated comprehensive isotachophoresis-capillary zone electrophoresis (ITP-CZE) system is described. The sample is focused in the first capillary by ITP and injected repeatedly into the second smaller diameter capillary for more rapid CZE separation. Since only small portions of the concentrated zones are sequentially injected for CZE separation, overloading was not observed. Moreover, the sensitivity is enhanced because all of the concentrated zones are analyzed and the results are summed. A single detector (only for the CZE dimension) is required, and accurate timing for CZE injection is not necessary. The system was evaluated using a mixture of angiotensins. The effect of addition of leading electrolyte at the junction of the ITP and CZE capillaries before each CZE run on comprehensive ITP-CZE peak area was studied, and leading electrolyte volumes between 7 and 11 microL led to the best sensitivity. Under optimized conditions, a detection limit of approximately 5 nM could be achieved by injecting 10 microL of angiotensin solution.     

大跨度钢索和CFRP索斜拉桥车桥耦合振动研究

以跨度600m～1400m的大跨度斜拉桥为对象,应用考虑拉索侧向振动影响的车桥耦合振动分析方法研究了钢索和CFRP索斜拉桥的交通振动响应,比较了车辆计算模型、行车速度对计算结果的影响,并分析了斜拉桥的动力冲击系数。研究结果表明,大跨度斜拉桥主梁的振动响应以静位移和长周期振动成分为主,拉索局部侧向振动不明显,车辆计算模型对结构振动响应的影响十分有限,行车速度的提高增加了结构的动力系数,两种拉索材料对斜拉桥在车辆荷载下的振动响应影响很小,斜拉桥的动力系数离散性大且与构件类型有关。