Methane: an open or shut case?

The author examines conflicting models, especially evidence from Price and Schoell in this issue (see comment), for the creation of ore deposits and the movement of petroleum. The Bakken formation in North Dakota is used as an example of a petroleum reservoir that has not migrated from its original site. Analysis of natural gases at the site indicates a difference in gas distribution between the Bakken site and migratory sites. Controversies are examined in the context of advances in fluid-flow calculations and high-temperature methanogenic reactions.     

Science:十大科学突破

正2015年12月17日,《Science》杂志评选出2015年度十大科学突破。基因剪刀CRISPR、埃博拉病毒疫苗、量子纠缠状态获证实等榜上有名。1基因剪刀CRISPR被誉为基因剪刀的CRISPR基因编辑技术荣登榜首,CRISPR全名为成簇的、规律间隔的短回文重复序     

Evolutionary biology: evidence for sympatric speciation?

Sympatric speciation is difficult to demonstrate in nature and remains a hotly debated issue. Barluenga et al. present a case of putative sympatric speciation for two cichlid species in the Nicaraguan crater lake Apoyo, but they overlook or reinterpret some key published information on the system. Although sympatric speciation is possible in theory, we show here that, when this information is taken into account, the results of Barluenga et al. do not provide conclusive evidence for sympatric speciation: this is because the null hypothesis of multiple invasion with introgression cannot be rejected.     

Palaeoclimatology: evidence for hot early oceans?

The oxygen isotopes in sedimentary cherts (siliceous sediments) have been used to argue that the Precambrian oceans were hot--with temperatures of up to 70 degrees C at 3.3 Gyr before present. Robert and Chaussidon measure silicon isotopes in cherts and arrive at a similar conclusion. We suggest here that both isotope trends may be caused by variations in seawater isotope composition, rather than in ocean temperatures. If so, then the climate of the early Earth may have been temperate, as it is today, and therefore more consistent with evidence for Precambrian glaciations and with constraints inferred from biological evolution.     

智能科学新范式：AI for Science的启示

<正>近日,科技部与自然科学基金委启动了“人工智能驱动的科学研究”专项部署工作,探索人工智能驱动的科学研究新范式,加速迈向交叉学科大发展时代,这对增强国家竞争力具有重要意义。在人工智能的促进下,新的科学研究范式正在形成。2024年年初,Open AI在官网正式发布了自定义GPT商店,意味着全球用户可以分享自己的自定义Chat GPT助手,属于大模型应用商店的时代悄然来临。基于此,     

PID Controller Stabilization for First-order Integral Processes with Time Delay

Due to the widespread application of the PID controller in industrial control systems, it is desirable to know the complete set of all the stabilizing PID controllers for a given plant before the controller design and tuning. In this paper, the stabilization problems of the classical proportionalintegral-derivative （PID） controller and the singleparameter PID controller （containing only one adjustable parameter） for integral processes with time delay are investigated, respectively. The complete set of stabilizing parameters of the classical PID controller is determined using a version of the Hermite-Biehler Theorem applicable to quasipolynomials. Since the stabilization problem of the singie-parameter PID controller cannot be treated by the Hermite-Biehler Theorem, a simple method called duallocus diagram is employed to derive the stabilizing range of the single-parameter PID controller. These results provide insight into the tuning of the PID controllers.     

Science in China Series B:Chemistry

EDITOR XU Guangxian (Hsu, Kwang-Hsien) College of Chemistry and Molecular Engineering Peking University Beijing 100871, China AIMS AND SCOPE Science in China Series B: Chemistry, an academic journal cosponsored by the Chinese Academy of Sciences and the N…     

Science in China Series B:Chemistry

EDITOR XU Guangxian (Hsu, Kwang-Hsien) College of Chemistry and Molecular Engineering Peking University Beijing 100871, ChinaAIMS AND SCOPE