NOx emission and thermal efficiency of a 300 MWe utility boiler retrofitted by air staging

Full-scale experiments were performed on a 300 MWe utility boiler retrofitted with air staging. In order to improve boiler thermal efficiency and to reduce NOx emission, the influencing factors including the overall excessive air ratio, the secondary air distribution pattern, the damper openings of CCOFA and SOFA, and pulverized coal fineness were investigated. Through comprehensive combustion adjustment, NOx emission decreased 182 ppm (NOx reduction efficiency was 44%), and boiler heat efficiency merely decreased 0.21%. After combustion improvement, high efficiency and low NOx emission was achieved in the utility coal-fired boiler retrofitted with air staging, and the unburned carbon in ash can maintain at a desired level where the utilization of fly-ash as byproducts was not influenced.

mtDNA Data Indicate a Single Origin for Dogs South of Yangtze River, Less Than 16,300 Years Ago, from Numerous Wolves

There is no generally accepted picture of where, when, and how the domestic dog originated. Previous studies of mitochondrial DNA (mtDNA) have failed to establish the time and precise place of origin because of lack of phylogenetic resolution in the so fa

Natural selection on EPAS1 (HIF2 alpha) associated with low hemoglobin concentration in Tibetan highlanders

By impairing both function and survival, the severe reduction in oxygen availability associated with high-altitude environments is likely to act as an agent of natural selection. We used genomic and candidate gene approaches to search for evidence of such genetic selection. First, a genome-wide allelic differentiation scan (GWADS) comparing indigenous highlanders of the Tibetan Plateau (3,200 3,500 m) with closely related lowland Han revealed a genome-wide significant divergence across eight SNPs located near EPAS1. This gene encodes the transcription factor HIF2 alpha, which stimulates production of red blood cells and thus increases the concentration of hemoglobin in blood. Second, in a separate cohort of Tibetans residing at 4,200 m, we identified 31 EPAS1 SNPs in high linkage disequilibrium that correlated significantly with hemoglobin concentration. The sex-adjusted hemoglobin concentration was, on average, 0.8 g/dL lower in the major allele homozygotes compared with the heterozygotes. These findings were replicated in a third cohort of Tibetans residing at 4,300 m. The alleles associating with lower hemoglobin concentrations were correlated with the signal from the GWADS study and were observed at greatly elevated frequencies in the Tibetan cohorts compared with the Han. High hemoglobin concentrations are a cardinal feature of chronic mountain sickness offering one plausible mechanism for selection. Alternatively, as EPAS1 is pleiotropic in its effects, selection may have operated on some other aspect of the phenotype. Whichever of these explanations is correct, the evidence for genetic selection at the EPAS1 locus from the GWADS study is supported by the replicated studies associating function with the allelic variants.

A 12-bit 300 MHz CMOS DAC for high-speed system applications

This paper describes a 12-bit 300 MHz CMOS DAC for high-speed system applications. The proposed DAC consists of a unit current-cell matrix for 8 MSBs and a binary-weighted array for 4 LSBs. In order to ensure the linearity of DAC, a double Centro symmetric current matrix is designed by using the Q(2) random walk strategy. To minimize the feedthrough and improve the dynamic performance, the drain of the switching transistors is isolated from the output lines by adding two cascoded transistors.

Etching Behavior of GaN/GaAs(001) Epilayers Grown by MOVPE

Wet etching characteristics of cubic GAN (c-GaN) thin films grown on GaAs(001) by metalorganic vapor phase epitaxy (MOVPE) are investigated. The samples are etched in HCl, H_3PO_4, KOH aqueous solutions, and molten KOH at temperatures in the range of 90～300 ℃. It is found that different solution produces different etch figure on the surfaces of a sample. KOH-based solutions produce rectangular pits rather than square pits. The etch pits elongate in [1(1-bar)0] direction, indicating asymmetric etching behavior in the two orthogonal <110> directions. An explanation based on relative reactivity of the various crystallographic planes is employed to interpret qualitatively the asymmetric etching behavior. In addition, it is found that KOH aqueous solution would be more suitable than molten KOH and the two acids for the evaluation of stacking faults in c-GaN epilayers.

古油松年轮记录的沈阳地区300年来的气候变化

本研究通过对沈阳清•昭陵、清•福陵和千山风景区树木年轮气候学考察和取样，共采集了103株古油松样本的树芯和轮盘。依据树木年轮气候学研究的规范做法建立了3地区的STD, RES, ARS三种类型的树轮宽度年表9个。并分析了不同采样点树木年轮所反映的气候信息，在此基础上重建了该区域近300年来的气候变化，开展了区域以及全球气候变化对比研究，以探讨沈阳地区近300年来气候变化的特点、规律和机制： （1）古油松年表与冬季和初春低温的关系较明显，1月的低温最显著，3种年表与冬季、春季和秋季的降水量的相关性均较显著。水汽压、相对湿度在入冬前、生长后期和易发生春旱的5-6月份对年轮宽度的影响表现突出。蒸发是上年全年、当年全年和当年绝大部分月份对油松生长起负效应的因素，其中5月最明显，但1、2月的蒸发量与油松当年的年轮宽度表现出正相关。油松年表的窄轮和窄化突变佐证了1650年以来的35次主要的旱灾年历史记录和59次干旱记录。 （2）本研究成功地检验了沈阳地区古油松年轮宽度年表对太阳活动，地磁活动，太平洋十年震荡和全球气温变化的响应。年轮宽度与这些影响因子均存在共同的周期变化和显著的线性关系。其中，年轮宽度对过去太阳活动和地磁的活动呈明显负相关关系，而且是多种抑、促效应的复合。所有结果表明沈阳城市古油松适于监测极度的诸如El Niño (La Niña)事件的全球环境变化和区域环境异常。 （3）本研究重建了沈阳地区1710-2004年12-1月的极端最低温，并指出其主要低温波动期，高温波动期；重建了沈阳地区1780-2004年1-6月的降水量，并统计了降水量反映的偏湿年份,，偏干年份；同时，分别重建了沈阳地区1780-2004年的年均水汽压、年蒸发量和年均相对湿度，并指出各重建结果所表征的旱涝年份。

近300年来中国森林的变迁

以清代以来史料为依据,在现代清查统计资料和前人研究成果的基础上,通过对森林变迁大体趋势及主要过程的客观把握,重新校订了1949年和1700年前人的估算数据,回溯估算了1750～1900年中国各省区每50年森林面积与森林覆被率值,并与现代森林清查资料衔接,分析1700～1998年近300年来中国森林变迁的时空特征。结果表明:近300年来中国现境内共减少森林面积约0.95×108ha,森林覆被率减少9.2个百分点,变化曲线呈先抑后仰;以1960s为界,此前呈加速递减态势,260年间减少森林面积达1.66×10

过去300年中国土地利用、土地覆被变化与碳循环研究

历史时期的土地利用与土地覆被变化是影响陆地生态系统碳循环的重要因素.过去300年间,我国土地利用与覆被发生了较大变化,林地面积迅速减小,垦殖扩张明显,均对陆地生态系统的碳循环产生了重要的影响.采用通过第一手历史文献资料重建的历史土地数据,分析了过去300年我国土地利用变化的主要特征,研究表明:在研究时段,耕地面积持续增加,从清前期1661年的60.78×106hm2增加到20世纪末的96.09×106hm2;森林面积从1700年的248.13×106hm2降至1949年的109.01×106hm2.受土地

过去300年中国部分省区耕地资源数量变化及驱动因素分析

通过对清代文献资料中田亩数据的分析,认为册载数据基本能够反映耕地面积的总体变化趋势和区域差别,但在总量上失之过低,为能更真实地反映耕地资源的变化实际,文中对其进行了相应处理。在此基础上,研究了300余年以来我国内地18省耕地资源的时空变化特点,总体而言,过去300年间研究区的耕地资源数量呈抛物线式变化,清前期的增长趋势明显,但至清晚期逐渐稳定下来,民国时期略有下降,新中国建立初期基本得到恢复。但是,此后又开始持续减少,过去300年间耕地资源的变化具有较为明显的区域性特点,东部地区的垦殖活动远较西部地区剧烈

Variations in the Summer Monsoon Rainbands Across Eastern China over the Past 300 Years

Chinese Academy of Sciences [KZCX2-YW-315-2]; National Natural Science Foundation of China [40701021, 40625002]