Quantification of Temperature-Dependent Charge Separation and Recombination Dynamics in Non-Fullerene Organic Photovoltaics

Transient optical spectroscopy is used to quantify the temperature-dependence of charge separation and recombination dynamics in P3TEA:SF-PDI₂ and PM6:Y6, two non-fullerene organic photovoltaic (OPV) systems with a negligible driving force and high photocurrent quantum yields. By tracking the intensity of the transient electroabsorption response that arises upon interfacial charge separation in P3TEA:SF-PDI₂, a free charge generation rate constant of ≈2.4 × 10¹⁰ s⁻¹ is observed at room temperature, with an average energy of ≈230 meV stored between the interfacial charge pairs. Thermally activated charge separation is also observed in PM6:Y6, and a faster charge separation rate of ≈5.5 × 10¹⁰ s⁻¹ is estimated at room temperature, which is consistent with the higher device efficiency. When both blends are cooled down to cryogenic temperature, the reduced charge separation rate leads to increasing charge recombination either directly at the donor-acceptor interface or via the emissive singlet exciton state. A kinetic model is used to rationalize the results, showing that although photogenerated charges have to overcome a significant Coulomb potential to generate free carriers, OPV blends can achieve high photocurrent generation yields given that the thermal dissociation rate of charges outcompetes the recombination rate.     

Applications of nanotechnology in oil and gas industry: Progress and perspective

Nanotechnology has been successfully implemented in many applications, such as nanoelectronics, nanobiomedicine, and nanodevices. However, this technology has rarely been applied to the oil and gas industry, especially in upstream exploration and production. The oil and gas industry needs to improve oil recovery and exploit unconventional resources. The cost of research and oil production is under immense pressure, and it is becoming more difficult to justify such investment when the crude oil price is weak and depressed. There is a widespread belief that nanotechnology may be exploited to develop novel nanomaterials with enhanced performance to combat these technological barriers. Increasing funding resources from governmental and global oil industry have been allocated to exploration, drilling, production, refining, and wastewater treatment. For example, nanosensors allow for precise measurement of reservoir conditions. Nanofluids prepared using functional nanomaterials may exhibit better performance in oil production processes, and nanocatalysts have improved the efficiency in oil refining and petrochemical processes. Nanomembranes enhance oil, water and gas separation, oil and gas purification, and the removal of impurities from wastewater. Functional nanomaterials can play an important role in the production of smart, reliable, and more durable equipment. In this review paper, we summarize the research progress and prospective applications of nanotechnology and nanomaterials in the oil and gas industry.     

Novel Direct Nanopatterning Approach to Fabricate Periodically Nanostructured Perovskite for Optoelectronic Applications

While indirectly patterned organic–inorganic hybrid perovskite nanostructures have been extensively studied for use in perovskite optoelectronic devices, it is still challenging to directly pattern perovskite thin films because perovskite is very sensitive to polar solvents and high‐temperature environments. Here, a simple and low‐cost approach is proposed to directly pattern perovskite solid‐state films into periodic nanostructures. The approach is basically perovskite recrystallization through phase transformation with the presence of a periodic mold on an as‐prepared solid‐state perovskite film. Interestingly, this study simultaneously achieves not only periodically patterned perovskite nanostructures but also better crystallized perovskites and improved optical properties, as compared to its thin film counterpart. The improved optical properties can be attributed to the light extraction and increased spontaneous emission rate of perovskite gratings. By fabricating light‐emitting diodes using the periodic perovskite nanostructure as the emission layers, approximately twofold higher radiance and lower threshold than the reference planar devices are achieved. This work opens up a new and simple way to fabricate highly crystalline and large‐area perovskite periodic nanostructures for low‐cost production of high‐performance optoelectronic devices.     

Sustainable Urban Development Issues in Chinese Transitional Cities: Hong Kong and Shenzhen

Post-colonial capitalist Hong Kong and rapidly developing Shenzhen in China's socialist market economy have both adopted a pro-growth strategy to cope with challenges imposed by a globalizing economy. This development philosophy has exerted tremendous pressure on both cities, pushing them further away from the path of sustainable urban development. Despite the policy rhetoric of pursuing sustainable development, both city governments have refrained from identifying and analysing sustainable urban development issues. While the top-down elite-dominated polities in Hong Kong and Shenzhen are working hard to attain world city status, both cities lack a sustainable development strategy. Without a critical rethink of the growth-first mentality, sustainability principles such as an ethical utilization of natural resources and aspirations for intra- and inter-generational equity are not put on the policy agenda. Despite recent efforts to clean up the environment, it is uncertain how these two growing cities will proceed as the global economy itself is starting to capitalize on sustainability efforts to further capital accumulation.     

Stiffness identification of laminated composite shafts

Distributions of bending stiffness along the spans of laminated composite shafts are determined via a non-destructive evaluation approach. The finite element method formulated on the assumption of uniform bending stiffness within each element is used in the deflection analysis of the shafts. Differences between measured and theoretically predicted deflections at any two points on a shaft are used to construct an error function for deflection. The identification of bending stiffness is formulated as a minimization problem in which the elemental bending stiffness are determined to make the error function a global minimum. A global minimization technique and a bounding method for establishing side constraints are presented to solve the above minimization problem. Experiments are performed to study the feasibility and applications of the proposed method.     

Hierarchical enrichment for bridging scales and mesh‐free boundary conditions

The finite‐element method, when used with a basis made up of piecewise polynomials, often requires the generation of a very fine computational mesh in order to capture localized solution phenomena such as boundary layers or near‐singularities. Enrichment of the basis with additional functions, obtained through analytical or experimental means, can allow for a coarser mesh and more accurate solution. We introduce an enrichment scheme in which an interaction or ‘bridging’ scale term is used to separate the basis formed by the enrichment functions from the original set of basis functions, in effect making the enrichment hierarchical. This separation of scales allows the simple application of essential boundary conditions. It also allows a quantification of the effects of the enrichment, leading to strategies for error estimation and control of the stiffness matrix condition number. We also find that this formulation allows for the simple application of essential boundary conditions for mesh‐free shape functions, which are notoriously problematic. We find that for multiple dimensions, care must be taken to derive a weak form which is truly consistent with the strong form on the essential boundary. Copyright © 2001 John Wiley & Sons, Ltd.     

Application of essential boundary conditions in mesh‐free methods: a corrected collocation method

Collocation methods for applying essential boundary conditions are defined as those methods in which conditions are enforced exactly at a discrete set of boundary nodes. In mesh‐free methods, this is usually accomplished by replacing rows of the matrix equations which result from discretization of the weak form with equations which ensure the enforcement of boundary conditions. In this paper, an inconsistency in this method is pointed out, and a correction is derived. Numerical test are done on one‐ and two‐dimensional equations; it is shown that convergence rates decrease with the use of the invalid traditional collocation and are restored with the corrected method. Copyright © 2000 John Wiley & Sons, Ltd.     

Reproducing kernel hierarchical partition of unity,Part I—formulation and theory

This work is concerned with developing the hierarchical basis for meshless methods. A reproducing kernel hierarchical partition of unity is proposed in the framework of continuous representation as well as its discretized counterpart. To form such hierarchical partition, a class of basic wavelet functions are introduced. Based upon the built‐in consistency conditions, the differential consistency conditions for the hierarchical kernel functions are derived. It serves as an indispensable instrument in establishing the interpolation error estimate, which is theoretically proven and numerically validated. For a special interpolant with different combinations of the hierarchical kernels, a synchronized convergence effect may be observed. Being different from the conventional Legendre function based p‐type hierarchical basis, the new hierarchical basis is an intrinsic pseudo‐spectral basis, which can remain as a partition of unity in a local region, because the discrete wavelet kernels form a ‘partition of nullity’. These newly developed kernels can be used as the multi‐scale basis to solve partial differential equations in numerical computation as a p‐type refinement. Copyright © 1999 John Wiley & Sons, Ltd.     

向服务业务模式转型——中国企业的可持续发展之路

<正>通向差异化竞争和可持续发展的新道路面对产品同质化、利润率不断下降、消费者需求日益严苛等难题,中国制造企业重生产轻服务的模式将难以维持。2008年开始的席卷全球的金融风暴引发了一系列的实体经济危机,制造企业急需走出一条通向差异化和可持续发展的新路。     

Experimental and computational validation of Hele-Shaw stagnation flow with varying shear stress

An in vitro flow model system with continuous variation of fluid shear stress can be used to test cell responses to a range of shear stresses. In this investigation, we validated such a flow system computationally for steady and unsteady flow conditions and experimentally for steady flow conditions. The unsteady flow validation is important for studying cells such as endothelial cells that experience unsteady flow conditions in their native environment. The system is capable of exposing cells in different regions of the chamber to steady or unsteady shear stress conditions with average values ranging linearly from 0 to 30 dyn/cm $^{2}$ . These tests and analyses demonstrate that the variable-width parallel plate flow system can be used to test the influence of a range of steady and unsteady fluid shear stress levels on cell activities.