7,041 research outputs found
The Sudbury-Serenitatis analogy and 'so-called' pristine nonmare rocks
The Serenitatis Basin is the one lunar basin from which we confidently identify a suite of samples as pieces of the impact melt sheet: the distinctive Apollo 17 noritic breccias. Recent studies of the Sudbury Complex indicate that its 'irruptive' is almost entirely of impact-melt origin, making it the closest terrestrial analog to the Serenitatis melt sheet. Any attempt to model the evolution of the Moon's crust should be compatible with the relatively well-understood Sudbury Complex. However, the Sudbury-Moon analogy might be a misleading oversimplification, if applied too rigidly. The cause of evolutionary differences between the Serenitatis impact melt and the Sudbury impact melt is discussed
Mars regolith versus SNC meteorites: Evidence for abundant crustal carbonates
Viking XRF analyses are compared with those for terrestrial and lunar basalt samples, and eucritic meteorites (of possible Mars origin). The comparison indicates depletion of Ca relative to Si in the Mars regolith. It is suggested that carbonate formation during a warmer, wetter epoch early in Mars' history could have been responsible
Value creation and change in social structures: the role of entrepreneurial innovation from an emergence perspective
Aim:
Our aim is to develop a more complete understanding of how processes that entrepreneurs perform interact with wider society and the causal effects of society on entrepreneurial behaviour and vice versa. We aim to show how entrepreneurial agency is put into effect in relation to the disruption of social structure and social change. This has implications for innovation and entrepreneurship policy and practice, and for entrepreneurship theory. We also investigate the role of ‘value’ in these processes.
Contribution to the literature
Our central argument is that emergent forms (or ‘emergents’) may be short lived (ephemeral) but have causal power on the performance of the actors in the system of inter-relationships in the innovation ecosystem. The emphasis on inter-related social processes and ontological stratification provides theoretical development of extant entrepreneurship theory on new venture creation (by explaining process), effectuation (by linking individualism and holism) and opportunity recognition (by deconstructing opportunity into anticipation, ontology and process).
Methodology
The paper takes an 'emergence' perspective as a way to understand entrepreneurial processes that give rise to innovation. The anticipation of value and the inter-relationship with social and organisational structures are fundamental to this perspective. A longitudinal analysis of a case study of the development of a new business model within an entrepreneurial firm is described. The case is followed through seven phases in which the relationship between process and emergent ontological status is shown to have destabilising and stabilising effects which produce emergent properties.
Results and Implications
One methodological contribution is framing how to conceptualise the empirical evidence. Emergents have causal effects on the anticipations of value inherent in their particular system of innovation. This causality is manifest as the attraction of resource in the firm; the stabilisation of the emergent constitutes strategy in the enterprise. A key role of the entrepreneurs in our case study was the creation and maintenance of evolving ontological materiality, as meaningful to themselves and to those with whom they interacted. In simple terms, they made things meaningful to people who mattered
How to find MACHOs in the Virgo Cluster
We discuss the feasibility of finding extra-galactic MACHOs by monitoring
quasars behind the Virgo cluster of galaxies. We show that with only a modest
observing programme one could detect several MACHOs in the mass range 1 X
10^{-5} to 2 X 10^{-2} solar masses if they make a significant contribution to
the mass of Virgo. The contamination by events from cosmologically distributed
MACHOs is estimated and is negligible if either the MACHO mass is greater than
about 10^{-4} solar masses or the quasar radius is greater than about 3 X
10^{15} cm.Comment: 5 pages, 1 figure, to appear in New Astronom
The Last Stages of Terrestrial Planet Formation: Dynamical Friction and the Late Veneer
The final stage of terrestrial planet formation consists of the cleanup of
residual planetesimals after the giant impact phase. Dynamically, a residual
planetesimal population is needed to damp the high eccentricities of the
terrestrial planets after the giant impact stage. Geochemically, highly
siderophile element (HSE) abundance patterns inferred for the terrestrial
planets and the Moon suggest that a total of about 0.01 M_Earth of chondritic
material was delivered as `late veneer' by planetesimals to the terrestrial
planets after the end of giant impacts. Here we combine these two independent
lines of evidence for a leftover population of planetesimals and show that: 1)
A residual planetesimal population containing 0.01 M_Earth is able to damp the
eccentricities of the terrestrial planets after giant impacts to their observed
values. 2) At the same time, this planetesimal population can account for the
observed relative amounts of late veneer added to the Earth, Moon and Mars
provided that the majority of the late veneer was delivered by small
planetesimals with radii <10m. These small planetesimal sizes are required to
ensure efficient damping of the planetesimal's velocity dispersion by mutual
collisions, which in turn ensures that the planets' accretion cross sections
are significantly enhanced by gravitational focusing above their geometric
values. Specifically we find, in the limit that the relative velocity between
the terrestrial planets and the planetesimals is significantly less than the
terrestrial planets' escape velocities, that gravitational focusing yields an
accretion ratio Earth/Mars~17, which agrees well with the accretion ratio
inferred from HSEs of 12-23. For the Earth-Moon system, we find an accretion
ratio of ~200, which is consistent with estimates of 150-700 derived from HSE
abundances that include the lunar crust as well as mantle component. (Abridged)Comment: accepted for publication in ApJ, 9 pages, 4 figures; minor
corrections, additional references adde
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