Experimental Investigations on Interaction of Two Drops by Thermocapillary-Buoyancy Migration

Experiments were performed, in a terrestrial environment, to study the migration and interaction of two drops with different diameters in matrix liquid under temperature gradient field. Pure soybean oil and silicon oil were used as matrix liquid and the drop liquid, respectively. The information on the motions of two drops was recorded by CCD camera system in the experiments to analyze the trajectories and velocities of the drops. Our experiments showed that, upon two drops approaching each other, the influence of the larger drop on the motion of the smaller one became significant. Meanwhile the smaller drop had a little influence on the larger one all the time. The oscillation of migration velocities of both drops was observed as they were approaching. For a short period the smaller drop even moved backward when it became side by side with the larger one during the migration. Although our experimental results on the behavior of two drops are basically consistent with the theoretical predictions, there are also apparent differences. 2006 Elsevier Ltd. All rights reserved. Keywords: Thermocapillary migration; Drop; Interaction; Oscillation 1. Introduction A bubble or drop will move when placed in another fluid with temperature gradient. This motion happens as a consequence of the variation of interfacial tension with temperature. Such a phenomenon is already known as Marangoni migration problem. With the development of microgravity science, bubble dynamics and droplet dynamics became a hot point problem of research because this investigation is very important for basic research as well as for applications in reduced gravity environment, such as space material science, chemical engineering and so on. Young et al. first investigated the thermocapillary migration of

Theoretical and experimental investigations of flexural wave propagation in periodic grid structures designed with the idea of phononic crystals

The propagation characteristics of fiexural waves in periodic grid structures designed with the idea of phononic crystals are investigated by combining the Bloch theorem with the finite element method. This combined analysis yields phase constant surfaces, which predict the location and the extension of band gaps, as well as the directions and the regions of wave propagation at assigned frequencies. The predictions are validated by computation and experimental analysis of the harmonic responses of a finite structure with 11 × 11 unit cells. The fiexural wave is localized at the point of excitation in band gaps, while the directional behaviour occurs at particular frequencies in pass bands. These studies provide guidelines to designing periodic structures for vibration attenuation.

Experimental and theoretical analysis of nondegenerate ultrabroadband chirped pulse optical parametric amplification

Experimental investigations of nondegenerate ultrabroadband chirped pulse optical parametric amplification have been carried out. The general mathematical expressions for evaluating parametric bandwidth, gain and gain bandwidth for arbitrary three-wave mixing parametric amplifiers are presented. In our experiments, a type-I noncollinear phase-matched optical parametric amplifier based on lithium triborate, which was pumped by a 5-ns second harmonic pulses from a Q-switched Nd:YAG operating at 10 Hz, seeded by a 14-fs Ti:sapphire laser at 800 nm, was presented. The 0.85 nJ energy of input chirped signal pulse with 57-FWHM has been amplified to 3.1 muJ at pump intensity 3 GW/cm(2), the corresponding parametric gain reached 3.6 x 10(3), the 53 nm-FWHM gain spectrum bandwidth of output signal has been obtained. The large gain and broad gain bandwidth, which have been confirmed experimentally, provide great potentials to amplify efficiently the broad bandwidth femtosecond light pulses to generate new extremes in power, intensity, and pulse duration using optical parametric chirped pulse amplifiers pumped by powerful nanosecond systems.

Investigation of kerosene combustion characteristics with pilot hydrogen in model supersonic combustors

Experimental investigations on the ignition and combustion stabilization of kerosene with pilot hydrogen in Mach 2.5 airflows were conducted using two test combustors, with cross sections of 30.5 x 30 and 51 x 70 mm, respectively. Various integrated modules, including the combinations of different pilot injection schemes and recessed cavity flameholders with different geometries, were designed and tested. The stagnation pressure of vitiated air varied within the range of 1.1-1.8 NiPa, while the stagnation temperature varied from 1500 to 1900 K. Specifically, effects of the pilot hydrogen injection scheme, cavity geometry, and combustor scaling on the minimally required pilot hydrogen equivalence ratio were systematically examined. Results indicated that the cavity depth and length had significant effects on the ignition and flameholding, whereas the slanted angle of the aft wall was relatively less important. Two cavities in tandem were shown to be a more effective flameholding mechanism than that with a single cavity. The minimally required pilot hydrogen equivalence ratio for kerosene ignition and stable combustion was found to be as low as 0.02. Furthermore, combustion efficiency of 80% was demonstrated to be achievable for kerosene with the simultaneous use of pilot hydrogen and a recessed cavity to promote the ignition and global burning.

激光诱发活塞的热负荷

活塞的热疲劳性能对柴油发动机的全寿命至关重要。由于能量有限和可控性差等缺点，现有实验系统均不能满意地进行活塞热负荷模拟实验。为此，提出并建立了一套激光诱发活塞热负荷的实验系统。该系统通过对激光束的空间整形，使之投射到活塞表面后诱发的温度场分布满足特定要求。基于PROFIBUS-DP现场总线技术实现了系统集成和实验过程的全反馈控制。针对活塞的典型热负荷条件，即高周热疲劳和热冲击分别进行实验，以模拟正常工作循环和“启动一停车”等热负荷或转速突变工况。通过设置加热一冷却周期或上限下限温度，可以获得相应的热负荷模拟实验效果。研究结果表明，采用经光束整形的激光进行活塞热负荷模拟实验具有周期短、可控性好等优点。 

The plastic instability behaviour of laser-textured steel sheet

As the production of a new technique that can offer both good formability and high image clarity for texturing metal sheet, laser-textured sheet has attracted the attention of many manufacturers and users. Among the many subjects to be studied, plastic instability behaviour of the laser-textured sheet is one of most important to understand its ability in extending material ductility and to appropriately control this technique. Experimental investigations are carried out in this paper to study the macroscopic behaviour and microstructural mechanism of the laser-textured sheet, and comparison is made with the normal sheet taken from the same coil of metal sheet. It is demonstrated that, the difference in the behaviour of plastic instability obviously shows tendency to delay strain localization and the onset of thickness necking. Shear banding and internal void damage are spread to a much wider region in the sheet being laser-textured. The prestrained microcraters enforced on the surface of the textured sheet act as hardening spots, which are likely to share out deformation and inhibit the increasing rate of voiding, and eventually favouring the ductility of the material used.

Notch sensitivity of circular rings subjected to impact loading

'Notch-sensitive regions' have been observed during a series of experimental investigations into the dynamic plastic behaviour and failure of thin-walled metallic radially notched circular rings with are-shaped supports subjected to concentrated impact loads. The experimental results show that the exterior notches at some regions have no effect on the deformation of the rings, but do have effect at the remaining regions. The notch-sensitive region is theoretically determined by using the equivalent structures technique; fairly good agreement has been reached between the simple theory and the experimental results. Both dimensional and theoretical analyses prove that whether a plastic hinge formed or not at the notched section does not depend on the mean radius of the ring and the input kinetic energy. It depends on the weak coefficient of the notched section and the angle of the support. Generally speaking, there are mainly three failure modes for a notched circular ring with are-shaped support under impact loading: Mode I, large inelastic deformation when the notch is outside the sensitive region, in this case the ring deforms as a normal one; Mode II, large inelastic deformation only at some part of the ring and tearing occurred at the notched sections; Mode III, large inelastic deformation and total rupture occurred at the notched sections. It is believed that the present study could assist the understanding of the dynamic behaviour and failure of other kinds of nonstraight components with macroscopic imperfections under impulsive loading.

Principles of flow field diagnostics by laser-induced biacetyl phosphorescence

A new method for measuring the density, temperature and velocity of N2 gas flow by laser induced biacetyl phosphorescence is proposed. The characteristics of the laser induced phosphorescence of biacetyl mixed with N2 are investigated both in static gas and in one-dimensional flow along a pipe with constant cross section. The theoretical and experimental investigations show that the temperature and density of N2 gas flow could be measured by observing the phosphorescence lifetime and initial intensity of biacetyl triplet (3Au) respectively. The velocity could be measured by observing the time-of-flight of the phosphorescent gas after pulsed laser excitation. The prospect of this method is also discussed.

Visualization of turbulence and internal waves in a stratified fluid

A new method for measuring the density, temperature and velocity of N2 gas flow by laser induced biacetyl phosphorescence is proposed. The characteristics of the laser induced phosphorescence of biacetyl mixed with N2 are investigated both in static gas and in one-dimensional flow along a pipe with constant cross section. The theoretical and experimental investigations show that the temperature and density of N2 gas flow could be measured by observing the phosphorescence lifetime and initial intensity of biacetyl triplet (3Au) respectively. The velocity could be measured by observing the time-of-flight of the phosphorescent gas after pulsed laser excitation. The prospect of this method is also discussed.

高超声速流动中侧向喷流干扰特性的实验研究

在高超声速(M=6)流动中,实验研究了侧向喷流的干扰特性,并探讨了喷流压力、攻角、迎风侧及背风侧喷流对侧向喷流干扰特性的影响.结果表明,在高超声速流动中,随喷流压力增大,喷流弓形激波与来流弓形激波相交,喷流前的高压区增大,而喷流后的低压区几乎不受影响,喷流的控制效果加强.与迎风侧喷流相比,背风侧喷流控制效果更好,这一趋势随攻角的增大更加明显.

超音速流动中侧向喷流干扰特性的实验研究

在超音速流动中,进行了侧向喷流干扰特性的实验研究,研究了喷流压力、攻角、迎风侧及背风侧喷流对侧向喷流干扰特性的影响.结果表明,随喷流压力增大,喷流前的高压区向前扩展,喷流的包裹作用加强.有攻角时,背风侧喷流前的高压区更大,喷流包裹作用的影响区域前移,喷流的控制效果更好,这一趋势随攻角的增大更加明显.

Adaptive Evolution of Digestive RNASE1 Genes in Leaf-Eating Monkeys Revisited: New Insights from Ten Additional Colobines

Pancreatic RNase genes implicated in the adaptation of the colobine monkeys to leaf eating have long intrigued evolutionary biologists since the identification of a duplicated RNASE1 gene with enhanced digestive efficiencies in Pygathrix nemaeus. The recent emergence of two contrasting hypotheses, that is, independent duplication and one-duplication event hypotheses, make it into focus again. Current understanding of Colobine RNASE1 gene evolution of colobine monkeys largely depends on the analyses of few colobine species. The present study with more intensive taxonomic and character sampling not only provides a clearer picture of Colobine RNASE1 gene evolution but also allows to have a more thorough understanding about the molecular basis underlying the adaptation of Colobinae to the unique leaf-feeding lifestyle. The present broader and detailed phylogenetic analyses yielded two important findings: 1) All trees based on the analyses of coding, noncoding, and both regions provided consistent evidence, indicating RNASE1 duplication occurred after Asian and African colobines speciation, that is, independent duplication hypothesis; 2) No obvious evidence of gene conversion in RNASE1 gene was found, favoring independent evolution of Colobine RNASE1 gene duplicates. The conclusion drawn from previous studies that gene conversion has played a significant role in the evolution of Colobine RNASE1 was not supported. Our selective constraint analyses also provided interesting insights, with significant evidence of positive selection detected on ancestor lineages leading to duplicated gene copies. The identification of a handful of new adaptive sites and amino acid changes that have not been characterized previously also provide a necessary foundation for further experimental investigations of RNASE1 functional evolution in Colobinae.

X-RAY-SCATTERING FROM A ROUGH-SURFACE AND DAMAGED LAYER OF POLISHED WAFERS

Theoretical and experimental investigations were performed to show the application of x-ray crystal truncation rod scattering combined with x-ray reflectivity in the measurements of surface roughness and near-surface damage of mechanochemically polished wafers. By fitting the measured crystal truncation rod curves it has been shown that polished wafers are divided into three parts -irregular steps on the surface, a damaged thin layer beneath the surface and a perfect bulk. The results show that the root mean square of the surface roughness of mechanochemically polished Fe-doped and/or S-doped InP wafers is one to two atom layers, and that the lateral correlation length of the surface roughness is about 3000-7500 Angstrom. The thickness of the damaged region is found to be about 1000 atom layers.