Origin of short period comets

Reasons for interest in the origin of short-period comets and the difficulties of computing their long-term dynamcal evolution are reviewed. The relative advantages of a source region in an extended inner core of the Oort cloud or a compact comet belt just beyond the planetary system are finely balanced, and it is premature to consider the problem solved. A complication is that some comets belonging to the Jupiter family may be part of a time-dependent system, possibly the remains of a giant comet such as Chiron which could have been part of the system 104 yr ago. The origin of short-period comets plays a pivotal role in many areas of solar system science: planet formation, the source of water (possibly life) on the terrestrial planets, the cratering record on the terrestrial planets and satellites of the outer planets, and the environmental impact posed by massive bodies and their decay products in the Earth's near-space environment.     

Extinguishing disaster in Alpine France: The fate of reforestation as technocratic debacle

In 19th-century France, concepts of alpine degradation formed the basis of ambitious state policies to reforest the Alps, Pyrenees, and Massif Central. Responding to the reality of large-scale flooding and to assumptions about the destructiveness of agro-pastoralism, both the Second-Empire and early Third-Republic regimes formulated legislation allowing for both voluntary and mandatory alpine reforestation projects. The latter regime's law of 1882 on the restoration and conservation of alpine lands was more conciliatory toward alpine agro-pastoralists; however, two case studies demonstrate that foresters attempted to overstep the limits of this more restrictive law. These actions conduced to rural protest which stymied the reforestation schemes. Although foresters could claim victory following the amended reforestation law of 1913, reduced budgets and a reduced forestry corps after World War One prevented its full implementation. Ultimately, geographers and some foresters revised scientific thinking about the history of deforestation, alpine ecology, and the place of humans in the mountains.     

A new proposition for redating the Mithraic tauroctony scene

Assuming that the figures of the central icon of the Mithraic cult – the scene of tauroctony (bull slaying) – represent equatorial constellations at the time when the spring equinox was placed somewhere between Taurus and Aries, it is difficult to explain why some equatorial constellations (Orion and Libra) were not included in the Mithraic icons A simulation of the sky at the times in which the spring equinox was in the constellation of Taurus, only a small area of spring equinox positions permits to exclude these two constellations, with all other representations of equatorial constellations (Taurus, Canis Minor, Hydra, Crater, Corvus, Scorpio) included. These positions of the spring equinox occurred at the beginning of the age of Taurus, and included Gemini as an equatorial constellation. Two of the main figures in the Mithraic icons are two identical figures, usually represented on the each side of the bull, wearing phrygian caps and holding torches. Their names, Cautes and Cautopates, and their looks may indicate that they represent the constellation of Gemini. In that case the main icon of Mithraic religion could represent an event that happened around 4000 BC, when the spring equinox entered the constellation of Taurus. Also, this position of equator contains Perseus as an equatorial constellation. Ulansey suggested that the god Mithras is identified with the constellation Perseus. In that case, all figures in the main scene would be equatorial constellations.     

Global volcanism, biological mass extinctions and the galactic vertical motion of the solar system

Summary. The recent findings of nearly matching long-term cyclicity in biological mass extinctions, geomagnetic reversals, impact cratering and other terrestrial processes have evoked a major controversy. We report here a compilation and analysis of major global magmatic episodes showing a significant enhancement of volcanic activity with a periodicity of 33 million years for the last 250 million years. These magmatic episodes match extremely well the best available astronomical estimates of the periodic (31 ± 5 Myr) galactic-disc crossing events during vertical motions of the solar system. These events also have a close linkage with the marine biological mass extinctions and other geological rhythms. It is argued that the prolonged volcanic activity, instead of impact cratering, may have been the more immediate primary cause for profound climatic and other environmental deterioration sufficient to create biological crises on a global scale. The volcanic periodicity scheme is well supported by the evidence of recent increases in volcanic activity. However, the alternative hypothesis of the death star 'Nemesis' can be rejected, since it does not explain the recent increase in volcanism and impact cratering during the last 4 ± 3 Myr in view of its quieter apehelion position lying beyond the Oort cloud of comets.     

突变理论在油气检测中的应用尝试

突变理论是现代非线性科学领域的一个重要分支,本文通过建立尖点突变模型和累加尖点突变模型,尝试性将突变理论应用于油气检测,提出突跳势、突跳间隔、突跳时间等参数,并通过实例分析,证明利用突跳参数进行油气检测的可行性。     

The fundamental role of giant comets in earth history

We discuss some fundamental aspects of Earth history as predicted by what has come to be called coherent rather than stochastic catastrophism. The latter essentially seeks to provide an understanding of terrestrial evolution in terms of occasional kilometre-plus impactors from the asteroid belt whereas the former recognises a far more complex extraterrestrial regime arising from the streams of sub-kilometre and kilometre-plus debris due to the disintegration of successive giant comets in sub-Jovian orbits. Periodicities of 15 Myr during the later Phanerozoic (i.e. 250 to 0 Myr BP) and 200 yr during the Holocene (i.e. 10,000 to 0 yr 1313) are likely fundamental signatures in the terrestrial record relating to the action of past and present giant cornets respectively.     

地震空区的定量判据

在中国，孕震空间已经比较广泛地应用于地震预报的实践，并多次取得实际预测强震的效果。但经过系统震例研究发现，利用孕震空间预报地震的虚报漏报率比较高。本文运用解决临界相变问题的重正化群方法所求出的孕震空间区可能发生失稳破裂，导致强震发生的判据对孕震空间的危险性作出进一步鉴别，并用突变论方法求解尖拐空变方程，预测孕震空区未来发生强震的时间和震级，并进一步确定孕震空区的危险性。对２６个中国大陆强有的孕震空