In an age when waste today means a lack tomorrow, making use of every available resource becomes more and more important. As coal is being used in greater and greater amounts to produce electricity, larger amounts of ash, by-product of coal, are produced. When coal is burned in a boiler, two kinds of ash by-product are produced, a heavy bottom ash and a fine-as-powder fly ash that is filtered and captured by precipitators. About 10 to 15 percent of the coal by-product is bottom ash which is used like sand on icy city streets and highways and also on highways as paving material. It is the fly ash, however, that is receiving the greater amount of attention. Fly ash may be used as an additive to concrete in the construction of dams, bricks, and roads, and can replace up to 20 percent of the cement used in concrete. As a by-product of burned coal, fly ash requires no additional expenditure of energy to be produced, while cement production requires great amounts of energy.In addition to using fly ash as a concrete additive, the technology is available to extract the main mineral components-aluminum, silicon, and magnetic. Today, extracting these components is a very expensive process, but the time may come when it is cheaper to extract these products from ash than to mine new supplies. What is a by-product of burned coal()
Aluminum, silicon, and magnetic.
B. Paving material.
C. Fly ash.
D. Concrete additive.
女孩,12岁。发热14天,T38~39℃,双手指指关节和掌指关节肿痛伴活动受限,两侧膝关节肿胀,以右侧明显,被动活动受限。无皮疹,浅表淋巴结无肿大。红细胞沉降串和C反应蛋白升高,血白细胞13×109/L,尿常规检查正常。 诊断首先考虑
A. 风湿热
B. 过敏性紫癜
C. 小儿类风湿病
D. 关节结核
E. 化脓性关节炎