Imaging in scattering media via the second-order correlation of light field

Imaging with the second-order correlation of two light fields is a method to image an object by two-photon interference involving a joint detection of two photons at distant space-time points. We demonstrate for the first time that an image with high quality can still be obtained in the scattering media by applying the second-order correlation of illuminating light field. The scattering effect on the visibility of images is analyzed both theoretically and experimentally. Potential applications and the methods to further improve the visibility of the images in scattering media are also discussed.Comment: 4 pages, 3 figure

Behaviour of alkali-activated concrete at elevated temperatures: A critical review

Alkali-activated concrete (AAC) is recognised as a novel sustainable construction material to substitute Portland cement concrete with superior thermal and mechanical performance. However, AAC would suffer significant deterioration when subjected to elevated temperatures due to different damage mechanisms, including thermal incompatibility caused by different thermal coefficients between matrix and aggregates, pore pressure build-up and phase transformation. This paper presents a systematic and comprehensive review on the behaviour of different types of AAC such as alkali-activated fly ash, alkali-activated slag, alkali-activated metakaolin and alkali-activated fly ash-slag systems at elevated temperatures in terms of phase stability and microstructural evolution as well as thermal and mechanical performance. The effective strategies for improving the high-temperature resistance of AAC are reviewed and discussed from the perspectives of AAC matrix, aggregates and fibre incorporation, with special focus on how these strategies can tackle different damage mechanisms. This paper summarises the recent advances in the field and identifies the remaining challenges and opportunities for future research

Two generalizations of ideal matrices and their applications

In this paper, two kinds of generalizations of ideal matrices, generalized ideal matrices and double ideal matrices. are obtained and studied, The concepts of generalized ideal matrices and double ideal matrices are proposed, and their ranks and maxima.linearly independent groups are verified.The initial motivation to study double cyclic matrices is to study the quasi cyclic codes of the fractional index. In this paper, the generalized form of the quasi cyclic codes, i.e. the {\phi}-quasi cyclic codes. and the construction of the generated matrix are given by the double ideal matrix

ENVIRONMENTAL METABOLOMICS OF FRESHWATER PHYTOPLANKTONS

Ph.DDOCTOR OF PHILOSOPH

Analysis of Transient Hydrogen Uptake by Metal Alloy Particles

This paper describes a new approach to solving the equations comprising the shrinking core model for diffusion and reaction of a chemical species in a solid spherical particle. The reactant adsorbs on the particle surface, diffuses into the particle\u27s interior, and reacts with the particle to form a solid product. The shrinking core model assumes a fast reaction rate compared to reactant diffusion so that the reaction is localized in the interfacial zone between the unreacted solid core and the surrounding shell of reacted product. Analytical solutions of the governing conservation equations usually invoke the pseudo-steady state (PSS) approximation which neglects the transient mass accumulation and diffusion-induced convection terms in the continuity equation for the diffusing reactant. However, small particle radii and slow reactant diffusion cast doubt on the validity of the PSS approximation. Dimensional analysis reveals an approximation that is less restrictive than PSS, yet enables a semi-analytical solution for the diffusing reactant distribution and interface velocity. For sufficiently large values of the surface mass fraction of the diffusing reactant, the PSS approximation leads to serious errors in the time dependence of the interface position and fractional conversion. However, our estimate of the surface mass fraction of hydrogen in LaNi5 particles suggests the validity of the PSS approximation for hydriding of metal alloy particles. The shrinking core model thus enables an estimate of hydrogen diffusivity in metal alloy particles

Effect of the nonlinear displacement-dependent characteristics of a hydraulic damper on high-speed rail pantograph dynamics

A new simplified parametric model, which is more suitable for pantograph–catenary dynamics simulation, is proposed to describe the nonlinear displacement-dependent damping characteristics of a pantograph hydraulic damper and validated by the experimental results in this study. Then, a full mathematical model of the pantograph–catenary system, which incorporates the new damper model, is established to simulate the effect of the damping characteristics on the pantograph dynamics. The simulation results show that large F const (saturation damping force of the damper during compression) and C (initial damping coefficient of the damper during extension) in the pantograph damper model can improve both the raising performance and contact quality of the pantograph, whereas a large C has no obvious effect on the lowering time of the pantograph; the nonlinear displacement-dependent damping characteristics described by the second item in the new damper model have dominating effects on the total lowering time, maximum acceleration and maximum impact acceleration of the pantograph. Thus, within the constraint of total lowering time, increasing the nonlinear displacement-dependent damping coefficient of the damper will improve the lowering performance of the pantograph and reduce excessive impact between the pantograph and its base frame. In addition, damping performance of the new damper model would vary with the vehicle speeds, when operating beyond the nominal-speed range of the vehicle, the damping performance would deteriorate obviously. The proposed concise pantograph hydraulic damper model appears to be more adaptive to working conditions of the pantograph, and more complete and accurate than the previous single-parameter linear model, so it is more useful in the context of pantograph–catenary dynamics simulation and further parameter optimizations. The obtained simulation results are also valuable and instructive for further optimal specification of railway pantograph hydraulic dampers. </p