Environmental change and seasonal behavior of mastodons in the Great Lakes region inferred from stable isotope analysis

We investigate seasonal variations in the diet and drinking water of four Great Lakes mastodon (Mammut americanum) specimens using stable isotope analysis of serially sampled inner-enamel bioapatite structural carbonate (δ¹³C_sc, δ¹⁸O_sc), and previously published bulk analyses. Isotopic analyses and thin section measurements showed that mastodon tooth enamel extension rates (~ 12–4 mm/yr, decreasing toward the cervix) were lower than those of mammoths or modern elephants. Mastodons had distinct and highly regular seasonal variations in δ¹³C_sc and δ¹⁸O_sc, which we interpret in the context of local glacial history and vegetation changes. Seasonal variations in δ¹⁸O were large but variations in δ¹³C were small, and may have been obscured if coarser sampling methods than our inner-enamel sampling approach were used. Thus, our approach may be particularly useful for understanding relatively small seasonal changes in δ¹³C within C₃ environments. The seasonal patterns, though not entirely conclusive, suggest that the Ontario mastodons did not migrate over very long distances. Rather, the climate and seasonal dietary patterns of mastodons within the region changed over time, from ~ 12,400 to 10,400 ¹⁴C yr BP (~ 15,000 – 12,000 cal yr BP). Insights gained using these methods can contribute to a better understanding of megafaunal extinctions and Paleoamerican lifeways.     

基于腾讯迁徙数据的中国城市群国庆长假城际出行模式与网络特征

城际出行具有时间依赖性,不同时间约束与特定时期的城际出行具有相异性,反映的出行模式与表达的地理空间联系规律具有差异性。迁徙大数据记录的人口移动实时记录为开展基于时间依赖的城际出行网络提供了可能。本文以全国 19个城市群为研究区域,利用腾讯平台提供的居民城际出行数据,对国庆长假期间（2016年10月1—7日）中国城市群城际出行时段变化特征、城际出行模式及其网络结构进行了研究。结果表明：① 黄金周城际出行具有明显的基于出行期、返程期和旅途期的时段变化规律;② 国庆长假期间的中国城市群城际出行分别形成了轴辐式、多中心与单中心3种城际出行模式; ③ 出行期、返程期的城际出行具有类似于春运人口流动的时空对称规律,城市群城际出行呈现出以主要城市群整体、城市群核心城市与邻近外围城市间的中短距离流动的长假出行特征,中西部城市群城际出行具有典型的“潮汐式”流动特征;④ 基于腾讯人口迁徙大数据,通过对黄金周期间出行期、返程期与旅途期的科学划分,较好地实现了国庆长假城际出行特征与模式的挖掘,同时也为长假城际交通管理与道路资源优化调配方案的制定提供支撑。     

Challenging climate change and migration discourse: Different understandings of timescale and temporality in the Maldives

This article draws on ongoing research in the Maldives to explore differences between elite and non-elite perceptions of climate change and migration. It argues that, in addition to variations in perceptions based on diverse knowledge, priorities and agendas, there exists a more fundamental divergence based upon different understandings of the timescale of climate change and related ideas of urgency and crisis. Specifically, elites tend to focus on a distant future, which is generally abstracted from people's everyday lived realities, and to utilise the language of a climate change-induced migration ‘crisis’ in their discussions about impacts in a manner not envisaged by non-elites. The article concludes that, rather than unproblematically mapping global, external facing narratives wholesale onto ordinary people's lives and experiences, there needs to be more dialogue between elites and non-elites on climate change and migration issues. These perspectives should be integrated more effectively into the development of policy interventions designed to support people in adapting to the impacts of global environmental change.     

‘There’s no future here’: The time and place of children’s migration aspirations in Peru

This article examines young Peruvians’ aspirations and the role of migration in their imagined futures, from a generational perspective. The data come from Young Lives, a long-term study of childhood poverty combining survey and qualitative approaches with children and their parents. The paper uses a biographical approach that sees migration as part of individual biographies as well as social structures and life course processes. The aim is to deepen understanding of the social contexts in which aspirations for and by children are generated, paying close attention to family migration histories, dynamic household contexts, and children’s migration networks. The analysis focuses on the time-spaces of migration aspirations, showing the way past, present and future are interconnected. It also emplaces aspirations by focusing on the way aspirations by and for children are constituted in and through particular places. The conclusion reflects on the role of poverty and argues that ‘aspirations’ are about much more than abstract ‘futures’; they orient actions in the present and say a great deal about young people’s current realities and relationships.     

衰减雷达波有限元偏移

高频雷达波在地球介质中有较强的衰减,反演中不可忽略．为此文中首先给出了含衰减项的雷达波的有限元方程及其偏移理论．用有限差分法或有限元法可正演合成雷达波资料,加入一定的扰动后用含衰减项的雷达波有限元方程做偏移,实例结果表明,考虑衰减项的偏移结果能使界面更好地归位,这为提高探地雷达地质解释的分辨率提供了可能性,为逐渐地实现符合雷达波自身动力学特点的处理系统奠定了基础．     

The origin of TNO 2004 XR190 as a primordial scattered object

Numerical integrations of the equations of motion of the giant planets and scattering particles show that there is a possible orbital itinerary that a particle may follow from a scattering mode up to a stable position near the orbit of 2004 XR₁₉₀. This orbital evolution requires that the particle gets trapped in a mean motion resonance with Neptune coupled with the Kozai resonance. Imposing migration on Neptune while a particle is experiencing both resonances can entail an escape from resonance at a low particle’s eccentricity. This eccentricity and the associated inclination are always similar to those of 2004 XR₁₉₀. I conclude that 2004 XR₁₉₀ was most likely a scattered object that went through those resonance processes and was eventually deposited at its current position. By the same argument, it is expected that there must exist several other objects with similar semimajor axis, eccentricity and inclination as those of 2004 XR₁₉₀.     

Transformation of Trojans into quasi-satellites during planetary migration and their subsequent close-encounters with the host planet

We use numerical integrations to investigate the dynamical evolution of resonant Trojan and quasi-satellite companions during the late stages of migration of the giant planets Jupiter, Saturn, Uranus, and Neptune. Our migration simulations begin with Jupiter and Saturn on orbits already well separated from their mutual 2:1 mean-motion resonance. Neptune and Uranus are decoupled from each other and have orbital eccentricities damped to near their current values. From this point we adopt a planet migration model in which the migration speed decreases exponentially with a characteristic timescale τ (the e-folding time). We perform a series of numerical simulations, each involving the migrating giant planets plus test particle Trojans and quasi-satellites. We find that the libration frequencies of Trojans are similar to those of quasi-satellites. This similarity enables a dynamical exchange of objects back and forth between the Trojan and quasi-satellite resonances during planetary migration. This exchange is facilitated by secondary resonances that arise whenever there is more than one migrating planet. For example, secondary resonances may occur when the circulation frequencies, f, of critical arguments for the Uranus-Neptune 2:1 mean-motion near-resonance are commensurate with harmonics of the libration frequency of the critical argument for the Trojan and quasi-satellite 1:1 mean-motion resonance . Furthermore, under the influence of these secondary resonances quasi-satellites can have their libration amplitudes enlarged until they undergo a close-encounter with their host planet and escape from the resonance. High-resolution simulations of this escape process reveal that ≈80% of jovian quasi-satellites experience one or more close-encounters within Jupiter’s Hill radius (R_H) as they are forced out of the quasi-satellite resonance. As many as ≈20% come within R_H/4 and ≈2.5% come within R_H/10. Close-encounters of escaping quasi-satellites occur near or even below the 2-body escape velocity from the host planet. Finally, the exchange and escape of Trojans and quasi-satellites continues to as late as 6-9τ in some simulations. By this time the dynamical evolution of the planets is strongly dominated by distant gravitational perturbations between the planets rather than the migration force. This suggests that exchange and escape of Trojans and quasi-satellites may be a contemporary process associated with the present-day near-resonant configuration of some of the giant planets in our Solar System.     

Benzo[b]naphthothiophenes and alkyl dibenzothiophenes: Molecular tracers for oil migration distances

The secondary migration of petroleum is one of the most critical geological processes responsible for the accumulation of hydrocarbons in a sedimentary basin. Pyrrolic nitrogen compounds such as carbazoles and benzocarbazoles are thought to be practical molecular indicators for estimating relative migration distances of oil. In light oils or condensates, however, considerable analytical errors are usually caused by low concentrations of NSO-compounds. Here we show that polycyclic sulfur aromatic hydrocarbons such as dibenzothiophene, C₁∼C₃ alkylated dibenzothiophenes and benzo[b]naphthothiophenes, which are present in relatively higher concentrations than the pyrrolic nitrogen compounds, exhibit changes in both absolute and relative concentrations that correlate with migration distances. The polycyclic sulfur aromatic hydrocarbons related parameters — benzo[b]naphtho[2,1-d]thiophene/{benzo[b]naphtho[2,1-d]thiophene + benzo[b]naphtho[1,2-d]thiophene} (abbreviated as [2,1]BNT/([2,1]BNT+[1,2]BNT) and the concentration of total dibenzothiophenes plus benzo[b]naphthothiophenes — are proposed by this paper to trace the oil migration distances.     

评述异常压力研究中的石油地质学新思想

在对异常压力的认识不断深化的过程中,凝结出许多新的概念和思想,为现代石油地质学理论注入了新的内容。关于超压生成与有机质成熟-生烃的关系虽有争议,但大多数主张超压对有机质成熟和生烃起抑制作用;在超压的背景下,生烃、排烃以及烃类的运移和聚集常呈现出幕式的特征;压力驱动是流体活动和油气运移的重要动力;动态运移通道是油气运移的新型通道;通常压力过渡带是油气聚集的有利场所;在超压的含油气盆地中,可能发现的非传统油气聚集有异常压力的气饱和封存箱、水力破裂-泥岩裂缝油气藏、烃水倒置的油气藏等。异常压力的储层具有相对独立性。     

Hydrocarbons and water in the Western Canada Sedimentary Basin — A tale of two fluids

Detailed petroleum system analysis allows the direction and extent of hydrocarbon flow to be assessed. In most parts of the Western Canada Sedimentary Basin, the major pulse of hydrocarbon generation and migration occurred as a result of the Laramide Orogeny in Late Cretaceous–Early Tertiary time. The distribution and chemistry of oils provide a detailed picture of fluid flow at this time with oil migration up to hundreds of kilometres observed. Hydrocarbon generation and migration mostly ceased once uplift of the basin commenced during Eocene time. As the basin evolved so did the hydrodynamic regime reflecting changes in topography, glaciation and other factors. This indicates possible problems with using present day hydrogeology to determine oil migration pathways although hydrogeology can help explain petroleum alteration.