Effects of hydrogen concentration on the emission and heat transfer of a premixed LPG-hydrogen flame

This paper describes an experimental study of the effect of hydrogen concentration on the emission and heat transfer characteristics of a laminar premixed LPG-hydrogen flame. The mole fraction of hydrogen in the fuel mixture was varied from 0% to 50%. The equivalence ratio of the fuel/air mixture was kept at stoichiometry and the mixture jet Reynolds number was fixed at Re = 1500 for most of the tests. The results show that upon varying hydrogen content in the fuel mixture, there is a corresponding change in the appearance, pollutant emissions and heat transfer characteristics of the flame.     

Linked multicontinuum and crack tensor approach for modeling of coupled geomechanics, fluid flow and transport in fractured rock

In this paper, we present a linked multicontinuum and crack tensor approach for modeling of coupled geomechanics, fluid flow, and solute transport in fractured rock. We used the crack tensor approach to calculate effective block-scale properties, including anisotropic permeability and elastic tensors, as well as multicontinuum properties relevant to fracture-matrix interactions and matrix diffusion. In the modeling, we considered stress dependent properties, through stress-induced changes in fracture apertures, to update permeability and elastic tensors. We evaluated the effectiveness and accuracy of our multicon-tinuum approach by comparing our modeling results with that of three independent discrete fracture network (DFN) models. In two of the three alternative DFN models, solute transport was simulated by particle tracking, an approach very different from the standard solute transport used in our multicon-tinuum modeling. We compared the results for flow and solute transport through a 20 m × 20 m model domain of fractured rock, including detailed comparison of total flow rate, its distribution, and solute breakthrough curves. In our modeling, we divided the 20 m × 20 m model domain into regular blocks, or continuum elements. We selected a model discretization of 40 × 40 elements (having a side length of 0.5 m) that resulted in a fluid-flow rate equivalent to that of the DFN models. Our simulation results were in reasonably good agreement with the alternative DFN models, for both advective dominated transport (under high hydraulic gradient) and matrix-diffusion retarded transport (under low hydraulic gradient). However, we found pronounced numerical dispersion when using larger grid blocks, a problem that could be remediated by the use of a finer numerical grid resolution, while maintaining a larger grid for evaluation of equivalent properties, i.e. a property grid overlapping the numerical grid. Finally, we encountered some difficulties in using our approach when element sizes were so small that only one or a few fractures intersect an element-this is an area of possible improvement that will be pursued in future research.     

Selection of funding schemes by a borrowing decision model: a Hong Kong case study

In financial decision‐making, a number of mathematical models have been developed for financial management in construction. However, optimizing both qualitative and quantitative factors and the semi‐structured nature of construction finance optimization problems are key challenges in solving construction finance decisions. The selection of funding schemes by a modified construction loan acquisition model is solved by an adaptive genetic algorithm (AGA) approach. The basic objectives of the model are to optimize the loan and to minimize the interest payments for all projects. Multiple projects being undertaken by a medium‐size construction firm in Hong Kong were used as a real case study to demonstrate the application of the model to the borrowing decision problems. A compromise monthly borrowing schedule was finally achieved. The results indicate that Small and Medium Enterprise (SME) Loan Guarantee Scheme (SGS) was first identified as the source of external financing. Selection of sources of funding can then be made to avoid the possibility of financial problems in the firm by classifying qualitative factors into external, interactive and internal types and taking additional qualitative factors including sovereignty, credit ability and networking into consideration. Thus a more accurate, objective and reliable borrowing decision can be provided for the decision‐maker to analyse the financial options.     

Spatial practice,conceived space and lived space: Hong Kong’s ‘Piers saga’ through the Lefebvrian lens

By applying the Lefebvrian lens, this paper tries to understand why unlike previous similar cases, the latest removal of the Star Ferry and Queen’s Pier was so controversial. To Lefebvre, embedded in ‘spatial practices’ that ‘secrete’ a place are two contradicting spaces: ‘conceived spaces’ produced by planners to create exchange values and ‘lived spaces’ appropriated by citizens for use values. Applying Lefebvre’s framework to examine the ‘Piers saga’, it is found that the pre‐Second World War (WWII) piers were ‘conceived’ by spatial practices of a colonial and racially segregated trading enclave. The public space in the commercial heart that housed the previous generations of piers was not accessible to the Chinese community, thus denying them opportunities to appropriate them and turn them into ‘lived’ spaces. It was only after WWII when the Government carried out further reclamation to meet the needs of an industrializing economy that inclusive public spaces were conceived in the commercial heart, enabling the general public to ‘appropriate’ them as ‘lived’ space. When the Government planned to remove this very first ‘lived’ space in the political and economic heart of the city to conceive further reclamation for the restructuring economy, the more enlightened citizens were determined to defend it.     

Development of thermally conductive polymer matrix composites by foaming‐assisted networking of micron‐ and submicron‐scale hexagonal boron nitride

Thermally conductive polymer matrix composite (PMC) foams with effective thermal conductivities (k_eff) higher than their solid counterparts have been developed for the first time. Using a material system consists of low density polyethylene and micron‐scale or submicron‐scale hexagon boron nitride platelets as a case example, this article demonstrates that foaming‐assisted filler networking is a feasible processing strategy to enhance PMC's k_eff, especially at a low hBN loading. Parametric studies were conducted to identify the structure‐to‐property relationships between foam morphology (e.g., cell population density, cell size, and foam expansion) and the PMC foam's k_eff. In particular, there exists an optimal cell size to maximize the PMC foam's k_eff for foams with up to 50% volume expansion. However, an optimal cell size is absent for PMC foams with higher volume expansion. X‐ray diffraction (XRD) analyses reveal that both the presence of hBN platelets and foam expansion promoted the crystallization of LDPE phase. Moreover, the XRD spectra also provide evidence for the effect of foam expansion on the orientation of hBN platelets. Overall, the findings provide new directions to design and fabricate thermally conductive PMC foams with low filler contents for heat management applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42910.     

Quality assurance of Chinese herbal medicines: Procedure for multiple‐herb extraction

A quality assurance (QA) procedure for multiple‐herb extraction, which takes into account the existence of common chemical markers and multiple‐herb‐extraction effects, has been developed for producing Chinese herbal medicines (CHMs) of consistent quality. The experimental method for determining related correlation function of the multiple‐herb‐extraction effect was designed. A systematic solution strategy was also developed to appropriately decompose the multiple‐herb extraction system into several subsystems for obtaining solution(s) and determining the overall behavior of the system. An example of QA of Danshen–Gegen (DG) decoction was used to demonstrate the QA procedure. An H9c2 cell assay was used to test the efficacy of consistent quality DG decoctions prepared by different herb combinations with different material costs of herbs. It was observed that a multiple‐herb‐extraction effect was present in the aqueous extraction of Danshensu and this effect was depended on the extraction solvent. The possible mechanism of this multiple‐herb‐extraction effect in the aqueous DG extraction was speculated to be the change of initial pH value of the aqueous extraction solvent by an unknown component from Gegen. The experimental chemical marker concentrations fell within ±10% of the specified chemical marker compositions by using the amount of herb from each herb class as predicted by the QA model. Furthermore, an H9c2 cell assay was used to test the efficacy of three consistent quality DG extracts, which were produced by different herb combinations with different material costs of herbs. The results showed that the three DG extracts provided consistent biological efficacy against menadione‐induced toxicity. This study extended a recently developed QA procedure of single‐herb extraction to multiple‐herb extraction. It provides a solution of QA in extraction, which is one of the most important unresolved problems in the modernization of traditional Chinese medicines. With this modified model and the companion experiments, the amount of herbs needed from different quality classes to produce a multiple‐herb formula CHM product decoction with consistent quality can be exactly determined. © 2014 American Institute of Chemical Engineers AIChE J 60: 4014–4026, 2014     

可编程器件为多种应用提供强大驱动力

几年前,超过半数的半导体消费均归功于企业用户,而如今,普通消费者已成为推动这一消费增长的主要推动力.从手机到电视,从计算机到汽车,普通消费者在半导体领域的需求占主导地位,市场竞争也比以往任何时候都更为激烈,成功与否取决于能否推出独树一帜的产品,而价格则是最重要的决定性因素.对系统制造商而言,这意味着必须展开激烈的市场"拼杀",而产品的生命周期则日益缩短.与此同时,市场细分进一步明显,过去的大规模市场被细分为更为狭窄的市场领域,只有提供具有各种不同特性、功能和地域特征的产品才能充分满足客户的特定需求.     

65nm半导体工艺发展策略

本文研究Altera在65nm工艺上的工程策略,介绍公司如何为客户降低生产和计划风险,并同时从根本上提高密度、性能,及降低成本和功耗.