Long-term decline of global atmospheric ethane concentrations and implications for methane

After methane, ethane is the most abundant hydrocarbon in the remote atmosphere. It is a precursor to tropospheric ozone and it influences the atmosphere's oxidative capacity through its reaction with the hydroxyl radical, ethane's primary atmospheric sink. Here we present the longest continuous record of global atmospheric ethane levels. We show that global ethane emission rates decreased from 14.3 to 11.3 teragrams per year, or by 21 per cent, from 1984 to 2010. We attribute this to decreasing fugitive emissions from ethane's fossil fuel source--most probably decreased venting and flaring of natural gas in oil fields--rather than a decline in its other major sources, biofuel use and biomass burning. Ethane's major emission sources are shared with methane, and recent studies have disagreed on whether reduced fossil fuel or microbial emissions have caused methane's atmospheric growth rate to slow. Our findings suggest that reduced fugitive fossil fuel emissions account for at least 10-21 teragrams per year (30-70 per cent) of the decrease in methane's global emissions, significantly contributing to methane's slowing atmospheric growth rate since the mid-1980s.     

Global variation in copy number in the human genome

Copy number variation (CNV) of DNA sequences is functionally significant but has yet to be fully ascertained. We have constructed a first-generation CNV map of the human genome through the study of 270 individuals from four populations with ancestry in Europe, Africa or Asia (the HapMap collection). DNA from these individuals was screened for CNV using two complementary technologies: single-nucleotide polymorphism (SNP) genotyping arrays, and clone-based comparative genomic hybridization. A total of 1,447 copy number variable regions (CNVRs), which can encompass overlapping or adjacent gains or losses, covering 360 megabases (12% of the genome) were identified in these populations. These CNVRs contained hundreds of genes, disease loci, functional elements and segmental duplications. Notably, the CNVRs encompassed more nucleotide content per genome than SNPs, underscoring the importance of CNV in genetic diversity and evolution. The data obtained delineate linkage disequilibrium patterns for many CNVs, and reveal marked variation in copy number among populations. We also demonstrate the utility of this resource for genetic disease studies.     

Strategies for mitigating an influenza pandemic

Development of strategies for mitigating the severity of a new influenza pandemic is now a top global public health priority. Influenza prevention and containment strategies can be considered under the broad categories of antiviral, vaccine and non-pharmaceutical (case isolation, household quarantine, school or workplace closure, restrictions on travel) measures. Mathematical models are powerful tools for exploring this complex landscape of intervention strategies and quantifying the potential costs and benefits of different options. Here we use a large-scale epidemic simulation to examine intervention options should initial containment of a novel influenza outbreak fail, using Great Britain and the United States as examples. We find that border restrictions and/or internal travel restrictions are unlikely to delay spread by more than 2-3 weeks unless more than 99% effective. School closure during the peak of a pandemic can reduce peak attack rates by up to 40%, but has little impact on overall attack rates, whereas case isolation or household quarantine could have a significant impact, if feasible. Treatment of clinical cases can reduce transmission, but only if antivirals are given within a day of symptoms starting. Given enough drugs for 50% of the population, household-based prophylaxis coupled with reactive school closure could reduce clinical attack rates by 40-50%. More widespread prophylaxis would be even more logistically challenging but might reduce attack rates by over 75%. Vaccine stockpiled in advance of a pandemic could significantly reduce attack rates even if of low efficacy. Estimates of policy effectiveness will change if the characteristics of a future pandemic strain differ substantially from those seen in past pandemics.     

工业烟气脱硫同时制取硫化氢的初步研究

提出一种无废烟气脱硫新方法。用硫化钠溶液洗脱工业烟气中二氧化硫，同时生成硫化氢。后者用Ｃｌａｕｓ反应可制取元素硫。反应过程为三阶段模式。第一阶段发生二氧化硫溶解和硫离子向硫氢根离子转变；第二阶段主要发生硫氢根离子向硫化氢转变同时吸收二氧化硫；第三阶段，溶液逐渐失去脱除ＳＯ２的能力。提高硫化钠初始浓度和反应温度或降低进气中二氧化硫含量，于提高Ｈ２Ｓ转化率有利。进气中二氧化硫分压增大，各阶段周期缩短。     

From Cars to Bicycles: an Ecosystem View of Montreal Traffic as a Wicked Problem

Systemic Practice and Action Research - In this paper, we share our reflections based on a process consultation project in collaboration with the Montreal Bicycle Advisory Committee. We put forward...     

高级动力学

高级动力学可以对动力学的分析工具作宽广且详尽的描写，可以讨论不同的强度和弱点，特别强调怎样才能彻底解决问题的技能。本书开始详尽评述矢量动力学，继而瞄准拉格朗日和哈密尔顿两方程以及诸如冲激响应、微分形式和可积性等不熟悉课题，还描述计算效能上超过传统经典法，特别当用于复杂的动力系统时效果更显著的重大改进。数值分析处理包括讨论数值稳定性和约束稳定两方面。本教科书每章附有不少工作例子和课后的思考问题。