Review on Applications of X-ray computed tomography for coal characterization : recent progress and perspectives

This research was funded by the National Natural Science Foundation of China (grant nos. 42130806, 41830427, 41922016 and 42102227).Peer reviewedPostprin

Microstructure Characterization Techniques for Shale Reservoirs : A Review

Funding This work was funded by the National Natural Science Foundation of China (Grant nos. U19B6003-03-01 and 42030804).Peer reviewedPublisher PD

Single Photon Emission from Single Perovskite Nanocrystals of Cesium Lead Bromide

The power conversion efficiency of photovoltaic devices based on semiconductor perovskites has reached ~20% after just several years of research efforts. With concomitant discoveries of other promising applications in lasers, light-emitting diodes and photodetectors, it is natural to anticipate what further excitements these exotic perovskites could bring about. Here we report on the observation of single photon emission from single CsPbBr3 perovskite nanocrystals (NCs) synthesized from a facile colloidal approach. Compared with traditional metal-chalcogenide NCs, these CsPbBr3 NCs exhibit nearly two orders of magnitude increase in their absorption cross sections at similar emission colors. Moreover, the radiative lifetime of CsPbBr3 NCs is greatly shortened at both room and cryogenic temperatures to favor an extremely fast output of single photons. The above findings have not only added a novel member to the perovskite family for the integration into current optoelectronic architectures, but also paved the way towards quantum-light applications of single perovskite NCs in various quantum information processing schemes

Ultrafast field-driven monochromatic photoemission from carbon nanotubes

Ultrafast electron pulses, combined with laser-pump and electron-probe technologies, allow for various forms of ultrafast microscopy and spectroscopy to elucidate otherwise challenging to observe physical and chemical transitions. However, the pursuit of simultaneous ultimate spatial and temporal resolution has been largely subdued by the low monochromaticity of the electron pulses and their poor phase synchronization to the optical excitation pulses. State-of-the-art photon-driven sources have good monochromaticity but poor phase synchronization. In contrast, field-driven photoemission has much higher light phase synchronization, due to the intrinsic sub-cycle emission dynamics, but poor monochromaticity. Such sources suffer from larger electron energy spreads (3 - 100 eV) attributed to the relatively low field enhancement of the conventional metal tips which necessitates long pump wavelengths (> 800 nm) in order to gain sufficient ponderomotive potential to access the field-driven regime. In this work, field-driven photoemission from ~1 nm radius carbon nanotubes excited by a femtosecond laser at a short wavelength of 410 nm has been realized. The energy spread of field-driven electrons is effectively compressed to 0.25 eV outperforming all conventional ultrafast electron sources. Our new nanotube-based ultrafast electron source opens exciting prospects for attosecond imaging and emerging light-wave electronics

Multiobjective constructal optimization of an insulating wall combining heat flow, strength and weight

a b s t r a c t For a vertical insulating wall, it is pursued in engineering design that taking the three requirements of heat insulation, mechanical strength and weight into account simultaneously, so we further develop the pioneer study of multidisciplinary constructal optimization presented in the previous paper [S. Lorente, A. Bejan, Combined 'flow and strength' geometric optimization: internal structure in a vertical insulating wall with air cavities and prescribed strength, Int. J. Heat Mass Transfer, 2002, 45(16): 3313e3320]. In this paper, thermal resistance per unit mass is introduced as the optimization objective, and a multidisciplinary and multiobjective constructal optimization is carried out based on the maximization of thermal resistance per unit mass with the global constraints, i.e. fixed external dimensions and prescribed mechanical strength. The results show that, the thermal resistance per unit mass of the insulating wall can approach its maximum with the corresponding optimal number of cavity under specified environmental condition (i.e. with specified natural convection effect). The bigger the strength is, the smaller the thermal resistance per unit mass is. For specified strength, the maximum thermal resistance per unit mass is insensitive to the change of the overall Rayleigh number group when the overall Rayleigh number group is much small; and then decreases monotonically with the increase of the overall Rayleigh number group when the overall Rayleigh number group is big, however, its decreasing amplitude decreases gradually. When heat flow, strength and weight are all taken into account, the 3-way optimization and selection (the maximization of thermal resistance per unit mass) of wall architecture requires higher degree of accuracy compared with the 2-way optimization and selection (the maximization of overall thermal resistance). This paper gives out an alternative scheme for the practical design of insulating wall, especially for the application case in which the weight of wall is limited strictly

The heat and mass transfer characteristics of superheated steam in horizontal wells with toe-point injection technique

Abstract Little efforts were done on the heat and mass transfer characteristics of superheated steam (SHS) flow in the horizontal wellbores. In this paper, a novel numerical model is presented to analyze the heat and mass transfer characteristics of SHS in horizontal wellbores with toe-point injection technique. Firstly, with consideration of heat exchange between inner tubing (IT) and annuli, a pipe flow model of SHS flow in IT and annuli is developed with energy and momentum balance equations. Secondly, coupled with the transient heat transfer model in oil layer, a comprehensive mathematical model for predicting distributions of pressure and temperature of SHS in IT and annuli is established. Then, type curves are obtained with numerical methods and iteration technique, and sensitivity analysis is conducted. The results show that (1). The decrease in SHS temperature in annuli caused by heat and mass transfer to oil layer is offset by heat absorbtion from SHS in IT. (2). SHS temperature in both IT and annuli increases with the increase in injection pressure. (3). IT heat loss rate decreases with the increases in injection pressure. (4). Increasing pressure can improve development effect

CONSTRUCTAL ENTRANSY DISSIPATION MINIMIZATION FOR "VOLUME-POINT" HEAT CONDUCTION BASED ON TRIANGULAR ELEMENT

By taking equivalent thermal resistance, which reflects the average heat conduction effect and is defined based on entransy dissipation, as optimization objective, the "volume to point" constructal problem based on triangular element of how to discharge the heat generated in a fixed volume to a heat sink on the border through relatively high conductive link is re-analyzed and re-optimized in this paper. The constructal shape of the control volume with the best average heat conduction effect is deduced. For the same parameters, the constructs based on minimization of entransy dissipation and the constructs based on minimization of maximum temperature difference are compared, and the results show that the constructs based on entransy dissipation can decrease the mean temperature difference better than the constructs based on minimization of maximum temperature difference. But with the increase of the number of order, the mean temperature difference does not always decrease, and there exists some fluctuations. Because the idea of entransy describes heat transfer ability more suitably, the optimization results of this paper can be put to engineering applica tion of electronic cooling