Q‐Morph: an indirect approach to advancing front quad meshing

Q‐Morph is a new algorithm for generating all‐quadrilateral meshes on bounded three‐dimensional surfaces. After first triangulating the surface, the triangles are systematically transformed to create an all‐quadrilateral mesh. An advancing front algorithm determines the sequence of triangle transformations. Quadrilaterals are formed by using existing edges in the triangulation, by inserting additional nodes, or by performing local transformations to the triangles. A method typically used for recovering the boundary of a Delaunay mesh is used on interior triangles to recover quadrilateral edges. Any number of triangles may be merged to form a single quadrilateral. Topological clean‐up and smoothing are used to improve final element quality. Q‐Morph generates well‐aligned rows of quadrilaterals parallel to the boundary of the domain while maintaining a limited number of irregular internal nodes. The proposed method also offers the advantage of avoiding expensive intersection calculations commonly associated with advancing front procedures. A series of examples of Q‐Morph meshes are also presented to demonstrate the versatility of the proposed method. Copyright © 1999 John Wiley & Sons, Ltd.     

The Potassium,Sodium, Magnesium,Calcium and Phosphate Nutrition of Sugarbeet (Beta vulgaris) Grown on Soils Containing Incorporated Straw

Between 1990 and 1992, a series of three experiments compared the effects of incorporating or removing straw from a total of five preceding cereal crops on the nutrient concentration, uptake and processing quality of sugarbeet. Incorporated straw increased K concentrations in tops and roots and increased total K uptake by c 40 kg ha^-1. Conversely, incorporated straw reduced Na concentrations and reduced total Na uptake by c 10 kg ha^-1. Straw incorporation had little effect on root processing quality, because whilst K impurities increased in the straw incorporated treatments, Na impurities were reduced. Generally, any effects of straw disposal method on concentration and uptake of phosphorus, calcium and magnesium were small and of little agronomic or economic significance. In the absence of regular soil analysis it is recommended that when straw has been incorporated that K fertiliser rates for beet are reduced by c 20 kg ha^-1. This is less than the allowance made for cereals. Also, contrary to the current cereal recommendation, there was no evidence for reducing P inputs when straw had been incorporated. © 1997 SCI.     

我国农作物秸秆综合利用现状

农作物秸秆是发展农村多种经营,发展生态农业,实现农业可持续发展的重要资源。目前我国农作物秸秆主要用作农村能源、养殖业饲料和还田。在工业利用方面,由于可供造纸的木材资源短缺,我国造纸工业形成了以草木并举的原料格局。因此,发展农作物秸秆的工业利用要注重农业生态,因地制宜、科学规划,适度利用。关键词:农作物秸秆;农业生态;农村能源;工业化利用     

Effect of increasing proportions of lignocellulosic cosubstrate on the single-phase and two-phase digestion of readily biodegradable substrate

The influence of different proportions of lignocellulosic substrate (cow manure with straw, CM) on the single-phase (conventional reactor) and two-phase (acidification/methanation with solids and liquid recirculation) digestion of a readily biodegradable substrate (fruit and vegetable waste, FVW) was investigated in order to determine the optimum cosubstrate ratio and the process best suited for codigestion. Both processes were fed initially with FVW, followed by FVW and CM at 80%:20% and 60%:40% (on volatile solids, VS basis) during an experiment run over eleven months. For the single-phase process, energy yield and VS destruction decreased by 11% and 9% with the 80%:20% FVW and CM ratio and by 16% and 17% with the 60%:40% feed ratio when compared to 100% FVW feed. For the two-phase process, energy yield and VS destruction decreased by 21% and 14% with 80%:20% feed ratio and by 48% and 33% with 60%:40% feed ratio compared to 100% FVW. Substrate solubilization in the acidification reactor was very efficient for all the feed proportions but it resulted in compounds other than volatile fatty acid (non-VFA COD) which were not easily amenable to methane generation. This led to a lower energy yield per kg of VS fed in the two-phase process compared to the single-phase process for the respective waste combination. For single-phase digestion, both 80%:20% and 60%:40% ratios were effective co-substrate combinations due to their higher energy yield. The two-phase process can be used for these ratios if higher VS reduction and a higher loading rate are the objectives.     

麦草新氨法蒸煮脱木素动力学研究

在合适的蒸煮工艺条件下,研究了麦草NH4OH-KOH-AQ法制浆过程脱木素动力学。实验结果表明,在大量脱木素阶段,脱木素反应对残余木素呈表观一级、对OH-呈0.38级,反应的活化能为44.12 k J/mol。脱木素速度方程为:-dL/dt=85.14exp(-5309/T)LCOH-0.38。     

Effect of sodium sulfite on acid pretreatment of wheat straw with respect to its final conversion to ethanol

A pretreatment process that combines dilute acid and sodium sulfite has been applied to wheat straw to study the effect of temperature (120–180 °C) and sodium sulfite concentration (0–3%) on the yield of glucose in subsequent enzymatic hydrolysis and ethanol production by fermentation. The results were compared with both dilute acid pretreatment (without Na₂SO₃ addition) and hot water pretreatment. Formation of furfural and hydroxymethylfurural, which can inhibit ethanol-producing microorganisms, were measured and the ethanol yield in a subsequent fermentation was evaluated. The results indicate that a combination of 180 °C, 30 min, 1% H₂SO₄ and 2.4% Na₂SO₃ during pretreatment produced the highest ethanol yield; 17.3 g/100 g dry weight of initial biomass, which corresponds to 75% of the theoretical yield from glucose. 28 mg of furan inhibitors (sum of furfural and hydroxymethylfurfural) per gram dry weight of initial wheat straw were generated under this condition. Increasing sulfite loading up to 2.4% decreased inhibitor formation, leading to increased delignification and preservation of cellulose from dissolution. On the other hand, an elevated temperature in combination with low pH reduced the amount of solid phase after pretreatment, increased the level of inhibitors and reduced the concentration of ethanol produced by fermentation.     

Methanogenic activity optimization using the response surface methodology,during the anaerobic co-digestion of agriculture and industrial wastes. Microbial community diversity

The anaerobic co-digestion of manure, agriculture and industrial wastes for methane production depends on the nutritional condition to develop the microbial community. The effect of each substrate concentrations, as well as their interactive effects on specific methanogenic activity and microbial community diversity were investigated in this work. A central composite design and the response surface methodology were applied for designing the anaerobic co-digestion batch test at 35 and 55 °C. It was analyzed the anaerobic sludge by specific methanogenic activity (SMA) and using molecular techniques (terminal restriction fragment length polymorphism, TRFLP). The results showed a significant interaction among the substrates and an enhancement of the methane production and SMA response caused by the three components. Rice straw had lower influence on SMA than clay residues, due to the mineral content and the beneficial ammonia nitrogen adsorbent properties of the latter. The optimum condition for mesophilic and thermophilic anaerobic co-digestion of pig manure, rice straw and clay mixture allowed SMA values of 1.31 and 1.38 gCH₄-COD/gVSSd⁻¹, respectively. The TRFLP analysis showed the effect of rice straw and clay addition on microbial community diversity at both temperatures. The acetotrophic methanogens belonging to the order Methanosarcinales (genera Methanosarcina and Methanosaeta) dominated in mesophilic condition, whereas at thermophilic conditions dominated Methanomicrobiales and Methanobacteriales order. The optimization allowed identifying the substrate interaction effects in a concentration range with a reduced number of experiments. Besides, the model validation proved to be useful for defining optimal combination of wastes in anaerobic system.     

Abscisic acid in straw residues from autumn-sown wheat

Wheat straw collected from the soil surface 9 weeks after the 1983 grain harvest contained the plant hormone abscisic acid (ABA). A 10 cm³ leachate from 1 g of straw is calculated to have contained sufficient ABA (1.5x10^?4 mol m^?3) to retard seedling root extension. In contrast, straw incorporated into surface soil shortly after harvest contained no detectable ABA 9 weeks after harvest. The concentration of ABA in the flag leaf increased during the 2 weeks before grain harvest in 1984. In this particularly wet autumn, ABA in surface straw decreased steadily to below the level of detection 7 weeks after grain harvest. Sephadex chromato-graphed fractions of aqueous extracts of fresh straw judged to contain ABA inhibited root extension of barley seedlings. These findings indicate causes of poor growth of cereal seedlings drilled into seed-beds with surface straw residues from the preceding crop.