基于归纳式学习法的通勤交通满意度指标研究

以评价通勤者对交通系统满意度为目的,建立通勤交通满意度指标.以问卷形式采集数据,采用归纳式学习方法,分析通勤者满意度等级与通勤时间之间的相关信息,得到以大于0.5证据权的出行时间区间为代表值的满意度指标.其中,通勤时间区间10～30 min为出行者最满意的通勤时间代表值.此结论从一个角度说明交通出行行为具有“可达性”与“移动性”的双重价值.     

A massive protocluster of galaxies at a redshift of z ≈ 5.3

Massive clusters of galaxies have been found that date from as early as 3.9 billion years (3.9 Gyr; z = 1.62) after the Big Bang, containing stars that formed at even earlier epochs. Cosmological simulations using the current cold dark matter model predict that these systems should descend from 'protoclusters'-early overdensities of massive galaxies that merge hierarchically to form a cluster. These protocluster regions themselves are built up hierarchically and so are expected to contain extremely massive galaxies that can be observed as luminous quasars and starbursts. Observational evidence for this picture, however, is sparse because high-redshift protoclusters are rare and difficult to observe. Here we report a protocluster region that dates from 1 Gyr (z = 5.3) after the Big Bang. This cluster of massive galaxies extends over more than 13 megaparsecs and contains a luminous quasar as well as a system rich in molecular gas. These massive galaxies place a lower limit of more than 4 × 10(11) solar masses of dark and luminous matter in this region, consistent with that expected from cosmological simulations for the earliest galaxy clusters.     

Anachronism and retrospective explanation: in defence of a present-centred history of science

This paper defends the right of historians to make use of their knowledge of the remote consequences of past actions. In particular, it is argued that the disciplinary cohesion of the history of science relies crucially upon our ability to target, for further investigation, those past activities ancestral to modern science. The history of science is not limited to the study of those activities but it is structured around them. In this sense, the discipline is inherently ‘present-centred’: its boundaries are determined, in part, by judgements inaccessible to the historical actors. Present-centredness of this sort, it is urged, should not be regarded as a problem; its methodological consequences are minimal.     

Science, truth and history, Part I. Historiography, relativism and the Sociology of Scientific Knowledge

Recently, many historians of science have chosen to present their historical narratives from the ‘actors’-eye view’. Scientific knowledge not available within the actors’ culture is not permitted to do explanatory work. Proponents of the Sociology of Scientific Knowledge (SSK) purport to ground this historiography on epistemological relativism. I argue that they are making an unnecessary mistake: unnecessary because the historiographical genre in question can be defended on aesthetic and didactic grounds; and a mistake because the argument from relativism is in any case incoherent.The argument of the present article is self-contained, but steers clear of metaphysical debates in the philosophy of science. To allay fears of hidden assumptions, the sequel, to be published in the following issue, will consider SSK’s prospects of succour from scientific realism, instrumentalism, and a metaphysical system of Bruno Latour’s own devising.     

Dark matter maps reveal cosmic scaffolding

Ordinary baryonic particles (such as protons and neutrons) account for only one-sixth of the total matter in the Universe. The remainder is a mysterious 'dark matter' component, which does not interact via electromagnetism and thus neither emits nor reflects light. As dark matter cannot be seen directly using traditional observations, very little is currently known about its properties. It does interact via gravity, and is most effectively probed through gravitational lensing: the deflection of light from distant galaxies by the gravitational attraction of foreground mass concentrations. This is a purely geometrical effect that is free of astrophysical assumptions and sensitive to all matter--whether baryonic or dark. Here we show high-fidelity maps of the large-scale distribution of dark matter, resolved in both angle and depth. We find a loose network of filaments, growing over time, which intersect in massive structures at the locations of clusters of galaxies. Our results are consistent with predictions of gravitationally induced structure formation, in which the initial, smooth distribution of dark matter collapses into filaments then into clusters, forming a gravitational scaffold into which gas can accumulate, and stars can be built.