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Revitalizing the moment distribution method: A fast and exact analysis of multibay, multi-story frames.
Get PDFThe conventional moment distribution method is revitalized with a new approach which requires only one-cycle of balance and carry-over and no iteration. For a continuous beam, the method begins by assuming the value of the balancing moment, say x, at the first joint. By invoking the moment equilibrium condition successively from the first towards the last joints, balancing and carry-over moments at other joints can be determined in terms of the unknown x without iteration. By means of moment equilibrium of the last joint, the unknown x can be solved exactly, regardless of the number of spans, and the final moment distribution of the whole structure can be easily obtained. Further, for multi-bay, single story frames, the analysis is carried out without the need to separate the analysis into two stages as in conventional MDM, and the final exact moments are found by solving two unknowns only, regardless of the number of bays. As such, the revitalized MDM is particularly advantageous for solving continuous beams and single-story frames with large number of spans or bays. Five examples are given herein to demonstrate the procedures and efficiency of the proposed method
Experimental study of a novel subcooling method based on liquid desiccant dehumidification for vapor-compression refrigeration systems.
No full textRefrigerant subcooling could increase the refrigerating capacity and potentially improve the performance of refrigeration systems. In this paper, a novel subcooling method is experimentally studied for the first time in a hybrid vapor compression refrigeration system. In this system, condensation heat (~40 °C) is used to drive an integrated subcooling cycle to subcool the refrigerant leaving the condenser, which significantly increases the system performance. Changes in system performance are measured as functions of the following variables: the mass flow rates of the dehumidification air, ambient air, dehumidification solution, regeneration solution, and spraying water. Comparisons are made between the proposed system and the traditional water-cooled chiller. The proposed system can achieve a larger degree of subcooling (15–20 °C); what’s more, it shows much higher performances than the traditional water-cooled chiller: COP and exergy efficiency of the chiller are improved by 18.6% and 27.9%, respectively. Performance of the integrated subcooling cycle is also evaluated; it has a low COP, with the maximum value of 0.13, due to the low-grade condensation heat; however, it has a pretty high exergy efficiency, with the maximum value of 0.28, which indicates the effective use of the low-grade heat. In addition, an economic analysis of the integrated subcooling cycle is made with a project life cycle of 15 years; the payback period varies from 2.4 to 3.2 years based on different electricity tariffs, and the savings to investment ratio is between 1.3 and 2.1, which indicates that the project is profitable
Occurrence of antibiotics and antibiotic resistance genes in soils fromwastewater irrigation areas in the Pearl River Delta region, southernChina
No full textThe occurrence and distribution of tetracycline (TC) and sulfamethazine (SMZ), and the corresponding antibiotic resistance genes (ARGs) were investigated in six agricultural sites in the Pearl River Delta (PRD) region in southern China. Irrigation water and irrigated soils at two different depths (0-10 and 10-20cm) were analyzed. The total concentrations of TC and SMZ in irrigation water ranged from 69.3 to 234ng/L and from 4.00 to 58.2ng/L, respectively, while the total concentrations of TC and SMZ in irrigated soils ranged from 5.00 to 21.9μg/kg and from 1.30 to 4.20μg/kg, respectively. After long-term irrigation with domestic and fishpond wastewater in the field, the residual TC and SMZ and their corresponding ARGs in soils were significantly higher in fishpond-irrigated soils (Dongguan and Shenzhen) than in domestic wastewater-irrigated soils (Foshan, Guangzhou, Huizhou and Zhongshan). The concentrations of antibiotics and their ARGs were significantly higher in irrigation water than in irrigated soils, which indicated that wastewater was the primary source of antibiotics in the soil environments. The domestic and fishpond wastewater were important repositories of antibiotics and their ARGs, which require effective treatment before their discharge into the environment. Other factors such as soil physicochemical properties, manure application, irrigation water sources and cropping patterns also affect the antibiotic concentrations and ARG abundances. The residual antibiotic concentrations statistically correlated with the corresponding ARGs in irrigation water and irrigated soils, both of which decreased with increasing soil depth, indicating that the concentration of antibiotics in the environment exerted a selection pressure on the microorganisms in the environment
Where\u27s the beef? 「肉」罷不能？
Get PDFChefs, scientists and food engineers look to the past and to the future in the race to find viable, sustainable and enjoyable alternatives to conventional animal products.
不少廚師、科學家和食品工程師都回顧過去、放眼未來，為尋找取代傳統動物肉類的食材絞盡腦汁