Improved inverted bubble method for measuring small contact angles at crystal-solution-vapor interfaces

We propose and evaluate an improvement of the inverted bubble method, originally proposed by McLachlan and Cox [Rev. Sci. Instrum. 46, 80 (1975)], a technique for measuring small contact angles at crystal-solution-vapor interfaces on a gas bubble under a solid immersed in a test solution. A simple experimental setup is used to evaluate the proposed method. We conclude that the method is suitable for measuring small contact angles with a minimum detectable angle of about 3 degrees . Improvements in instrument design are proposed to lower the detection limit to 0.5 degrees or below.     

Analysis of the field of a plane SH-wave scattered by a finite crack on the interface of materials

We solve the problem of diffraction of plane elastic SH-waves on a crack of finite width located in the plane interface of two different perfectly joined isotropic elastic materials. The problem is solved by the Wiener-Hopf method. An approximate solution of the Wiener-Hopf equation is obtained. The numerical results in the far-field zone are presented for a broad frequency band. The specific features of distribution of the radiation field in the zone of critical angles are analyzed. The probability of excitation of lateral waves is investigated and the possibility of detection of defects is discussed. A simple experimental procedure is proposed for the NDT evaluation of crack width in a test bench based on measuring the modulus of the field of displacements in the zone of critical angles. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 6, pp. 5–16, November–December, 2006.     

摄动法研究硬盘磁头滑块动态飞行特性

硬盘工作时,磁头滑块飞行在磁盘上方,其动态飞行特性对硬盘工作性能有重要影响。该文利用摄动法推导了磁头滑块的气膜刚度和阻尼摄动方程,且通过有限体积法进行求解,获得了初始摄动条件下的气膜刚度和阻尼矩阵。结合磁头滑块动力学方程,研究了扰动速度、扰动俯仰角和扰动侧倾角对磁头滑块动态飞行特性的影响。研究结果表明:①扰动速度会导致磁头滑块向磁盘表面作竖直方向的移动,增加了与磁盘接触碰撞的风险;②扰动俯仰角或侧倾角的增加都会导致磁头滑块振动幅度的增加,但扰动俯仰角更容易引起磁头滑块的振动。     

Detection of outliers in gas emissions from urban areas using functional data analysis

In this work a solution for the problem of the detection of outliers in gas emissions in urban areas that uses functional data analysis is described. Different methodologies for outlier identification have been applied in air pollution studies, with gas emissions considered as vectors whose components are gas concentration values for each observation made. In our methodology we consider gas emissions over time as curves, with outliers obtained by a comparison of curves instead of vectors. The methodology, which is based on the concept of functional depth, was applied to the detection of outliers in gas omissions in the city of Oviedo and results were compared with those obtained using a conventional method based on a comparison of vectors. Finally, the advantages of the functional method are reported.     

Aspects of reliability design of hydrocarbon offshore platforms

The paper is a critical examination of Reliability and Safety aspects relating to Offshore Hydrocarbon Platforms. It aims at providing appropriate Design Criteria and proposing reasons for the implementation of more qualified gas detection systems technologies. Criteria generally adopted for manned platforms, associating an alarm to the detection of gas, cannot be extrapolated to unmanned platforms, especially when the topside is not realised on the basis of a completely ‘open’ layout.

The paper discusses reliability design criteria for manned platformsbased on operational design experience and discusses design improvements and reasons for the greater reliability required from gas detection systems when applied to unmanned platforms.     

基于光声原理的火灾复合气体探测技术

监测燃烧过程中产生的气体（主要是CO）来探测火灾逐渐成为火灾探测中的一个重要领域。各种现有的气体传感器灵敏度比较低，不利于火灾的早期报警,利用基于光声原理的复合气体探测技术来进行火灾探测，能极大地提高探测器的灵敏度。将CO和CO2的检测结合起来，可降低探测器的误报率，有利于提高早期报警。     

ADHESIVELY BONDED COMPOSITE IOSIPESCU SPECIMENS WITHOUT SINGULAR STRESS FIELDS

The asymptotic singular stress fields at bi-maSerial wedge corners in adhesively bonded composite losipescu specimens have been studied using two-dimensional finite-element techniques. In particular, the singular powers of the fields have been analyzed using the finite-element iterative method. Different combinations of the elastic properties of the composite adherends have been considered, taking into account various volume fractions of fibers as well as different fiber orientations with respect to the adherend/adhesive interface. It has been shown that there are critical angles of the interfaces that separate the regions with positive and negative singular powers. This creates stress fields that are not singular in nature. It appears that the critical angles are dependent on the elastic properties of the composite adherends. In the second part of this work, the critical angle approach has been applied to the design of adhesively bonded composite losipescu specimens free from singular stress fields at their bi-material wedge corners. The samples will not develop singular stress fields either in shear or under biaxial shear-dominated loading conditions.     

Oblique hypervelocity impacts into graphite

Investigations have been conducted into the morphology of craters formed by impacts of aluminium and HDPE projectiles at oblique angles to graphite target plates. The experiments were conducted with a two-stage gas gun capable of launching projectiles of differing density and strength to speeds of about 6 kms⁻¹ at right angles into target plates. It was found that, as the impact angle is decreased from the normal, the crater dimensions scaled as the normal component of the impact velocity as predicted by the ‘2/3 power law’ until a critical normal velocity was reached below which the conditions for a hypervelocity impact no longer apply. In this regime, new scaling laws were derived for the crater dimensions. It was also possible to identify a fragmentation angle below which the projectile remains intact as it ricochets across the target surface.     

不同波长激光对计算全息位相光栅空间衍射光束分辨率的影响

针对用于激光阵列探测系统中的计算全息位相光栅，给出了在不同波长激光入射的情况下，衍射光束的空间分辨率随不同入射角的变化情况。用实验验证了用可见光代替红外激光进行初步测试与分析的可行性，为用于红外系统的整形光栅的测试提供了简捷，便利的实验方法。     

Thickness measurement of a thin-film layer on an anisotropic substrate by phase-sensitive acoustic microscope

Complex V(z) curves for single thin-film layers on anisotropic substrates are studied both experimentally and theoretically, and the application of V(z) measurement to the determination of film thickness on anisotropic substrates is discussed. Complex V(z) curves for aluminum layers (with thicknesses between 0.5 and 2 mum) on a silicon wafer have been calculated. The inverse Fourier transform of the V(z) curves, which corresponds to the reflection coefficient, shows sharp changes at critical angles of pseudosurface waves, pseudo-Sezawa waves, and Rayleigh surface waves. These critical angles strongly depend on the thickness. Complex V(z) curves for these specimens have been measured using a phase-sensitive acoustic microscope with a point focus lens at 400 MHz. The critical angles of the surface waves obtained from the measured V(z) curves are in good agreement with those obtained from the calculated V(z) curves. On the basis of this result, it is shown that the V(z) measurement is applicable to the determination of film thickness on an anisotropic substrate.     

Measurement of concentration pulsations in a shear turbulent flow by the method of averaged Talbot images

The method of two-exposure Talbot photography has been adapted to analysis of the flow structure in a two-dimensional turbulent submerged jet of helium flowing out into an air space and in a gas flow behind the incident shock wave in a shock tube. Measurement of the local shift of the intensity maxima in the time-averaged Talbot image made it possible to determine, for the cases investigated, the two-dimensional array of angles of refraction of light with an error to 5%. The distribution of the averaged refractive index of the medium and the concentration of the gas over the flow field has been calculated by integration of the distributions obtained. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 1, pp. 49–54, January–February, 2008.     

Development, validation, and application of a method for quantification of methylmercury in biological marine materials using gas chromatography atomic emission detection

A gas chromatographic method was developed for the quantification of alkylmercury species using microwave-induced plasma atomic emission detection (GC-AED). The column conditioning and analyte derivatization required for previous methods were found to be unnecessary for stable, accurate, and sensitive element-specific detection using GC-AED. Chromatographic and detection parameters such as stationary phase type, stationary phase film thickness, GC column dimensions, helium mobile phase column head pressure, detector makeup gas flow rate, and detector reagent gas type and flow rate were found to significantly affect analyte response. The detection limit for the optimized GC-AED conditions was 0.8 pg (0.1 pg/s) of methylmercury chloride (as mercury). A solid-liquid extraction procedure with preparative gel permeation chromatography cleanup and GC-AED analysis was used to quantify methylmercury in a variety of complex matrix marine materials. The methylmercury quantification method was validated with four marine certified reference materials (CRMs). The method was then applied to 13 standard reference materials, CRMs, and control materials for which no certified reference values for methylmercury have been determined. Four National Institute of Standards and Technology Standard Reference Materials and one control material, which were analyzed using the GC-AED method, were also analyzed by two other laboratories using independent methods to further validate the method.     

Relations between the critical angles and the optical tensor of a biaxial material

The behavior of the critical angles between a high-index isotropic medium and a biaxial crystal with arbitrary orientation of the optical tensor has been theoretically analyzed and numerically modeled. The results indicate that, as the biaxial crystal is rotated around an axis perpendicular to the interface, two critical angles appear, corresponding to the excitation of two eigen modes, which periodically vary with a period of pi. An optical procedure for fully characterizing the optical tensor of a biaxial crystal is suggested on the basis of the twist-angle dependence of these critical angle. This procedure simply requires the measurement of the p- to s-conversion reflectivity against the sample rotation angle, with just one polished surface of a biaxial crystal.     

Measurement of small rotation angles by using a parallel interference pattern

We propose a method for measuring rotation angles by using a parallel interference pattern. At two points on a parallel interference pattern reflected by an object, we detect phase changes in the reflected parallel interference pattern caused by rotations of the object. A high sensitivity, or a high ratio of the phase change to the rotation angle, 17 mrad/arcsec, can be achieved by determining the positions of two detection points. A high spatial resolution of ~0.5 mm is also obtained. We analyze the measurement error caused by the alignment of the parallel interference pattern and a random measurement error caused by the phase detection. The theoretical analyses and the experimental results make the characteristics of the method clear and show that the method has an accuracy of 0.2 arcsec for small rotation angles.     

Numerical analysis of critical state behaviors of granular soils under different loading conditions

Discrete element method is used to simulate granular assembly behaviors with different initial conditions under three different loading conditions—plain strain, conventional triaxial compression, and direct shear. Different deformation modes of specimens with different conditions are presented. Some important parameters of the critical state theory are investigated. Uniqueness of the critical state line is checked which shows that there is no a unique critical state line for specimens with different initial void ratios under different loading conditions. Frictional angles and dilation angles of specimens with different conditions at critical state are compared. Void ratios and coordination numbers of specimens at critical state are studied. Anisotropies of the particle orientation and normal contact force at initial state, critical state, as well as the evolutions during shearing are analyzed. The anisotropy is shown to have significant effects on the soil behaviors and is related to the non-uniqueness of the critical state line. The developed numerical models can be used to study the micromechanics and microstructure of the specimen subjected to different loading conditions in the future.     

Mechanics of minor ship collisions

A structural method is presented by which the critical velocity for a minor collision of a ship striking another ship midships at right angles can be determined rather realistically with a minimum of computational effort. The velocity of the striking ship is defined as critical for a minor collision when the side wall of the struck ship just ruptures. This means the possibility of an oil spill in an oil tanker.The proposed method takes into account the deformability of both collision opponents. The energies absorbed in both ships, up to rupture of the struck ship hull, are computed using internal collision mechanics. The critical velocity can then be determined using external collision mechanics.The method is used for the collision of two equal oil tankers of 141,000 TDW with bulbous bows. The critical velocity was found to be 6.8 knots.     

Evaluation of Microwave-Assisted Process technology for HAPSITE's headspace analysis of volatile organic compounds (VOCs)

The use of microwave energy as a heating source for the field-based headspace sampling and the subsequent determination of various volatile organic compounds (VOCs) using a field-portable HAPSITE gas chromatograph-mass spectrometer has been evaluated. A significant advantage in time reduction has been observed when using microwave energy when compared to conventional resistive-based heating. Such time savings are critical in field operations involving equipment such as the HAPSITE where non-routine sampling is commonly performed and very quick turnaround time is usually needed. Further, the technology also showed significant improvements in terms of sensitivity, thus suggesting its applicability to a broader range of compounds and detection levels than current technologies.     

Development of a solid-phase microextraction gas chromatography/tandem mass spectrometry method for polybrominated diphenyl ethers and polybrominated biphenyls in water samples

Solid-phase microextraction has been applied for the first time to the determination of trace concentrations of some brominated flame-retardant compounds (BFRs) in water samples. For the development of the method, six polybrominated diphenyl ethers and two polybrominated biphenyls were considered as target analytes. The factors expected to influence the extraction process are fully discussed. Quantification has been performed by gas chromatography/tandem mass spectrometry using an ion trap mass analyzer. This is also the first time that tandem mass spectrometry is applied with these analytes. Unlike conventional methods for BFR analysis, which involve solvent extraction and several cleanup steps before gas chromatography, the proposed method uses headspace extraction and hard contamination of the chromatographic system is prevented. In addition, tandem mass spectrometry provides selectivity and sensitivity in the detection process. The method performs well achieving good linearity (R(2) > 0.997), precision, and detection limits (S/N = 3) ranging from 7.5 to 190 pg/L. The method has been applied to a variety of water samples.     

基于车道线斜率的车道偏离检测

针对结构化道路上运动车辆的车道偏离检测问题,采用单目视觉作为感知手段,分别从针孔模型下摄像机成像的空间几何关系和图像中车道线消失点的位置特点两个方面出发,推导出车辆直行情况下车道偏离率与两侧车道线斜率比之间的简单函数关系,该函数与摄像机内外参数无关。同时完成了在摄像机不同方向角下的车道偏离率测量试验,结果表明由于行车方向瞬时变化引起的摄像机方向角微小改变对车道偏离检测的影响可以忽略。道路现场试验结果表明,上述视觉测量方法得到的车道偏离率与手工实测结果相比,其相对误差小于5%。基于车道线斜率的单目视觉检测方法避开了繁琐的摄像机参数标定过程,达到了较高的车道偏离检测精度。     

预应力混凝土组合箱梁桥波形钢腹板的屈曲分析

通过解析方法及空间有限元方法研究波形钢腹板预应力混凝土组合箱梁桥在各种腹板尺寸参数时,对钢腹板的剪切屈曲应力或临界荷载及屈曲模态的影响。计算及分析结果表明:腹板高度越大,其它参数不变时,屈曲临界荷载随折叠角度的增大而呈抛物线形的增加幅度越小;当腹板折叠角度越大,腹板越厚,其它参数不变时,屈曲临界荷载随着腹板高度的增加呈抛物线形的下降幅度越大。因此,在钢腹板的5个参数中,腹板高度及腹板折叠角度两个参数对腹板的剪切屈曲稳定和屈曲模态起着关键的作用,不能随意用腹板的高厚比来衡量屈曲应力的大小。