16,032 research outputs found
Proof of the volume conjecture for Whitehead chains
We prove the volume conjecture for an infinite family of links called
Whitehead chains that generalizes both the Whitehead link and the Borromean
rings.Comment: 11 pages, 1 figure. See also
http://www.science.uva.nl/~riveen/papers.html New in version two is a
computation for the constant term in the asymptotic expansion. The proof of
lemma 5 has been omitted because it is almost the same as that of lemma
How micropatterns and air pressure affect splashing on surfaces
We experimentally investigate the splashing mechanism of a millimeter-sized
ethanol drop impinging on a structured solid surface, comprised of
micro-pillars, through side-view and top-view high speed imaging. By increasing
the impact velocity we can tune the impact outcome from a gentle deposition to
a violent splash, at which tiny droplets are emitted as the liquid sheet
spreads laterally. We measure the splashing threshold for different
micropatterns and find that the arrangement of the pillars significantly
affects the splashing outcome. In particular, directional splashing in
direction in which air flow through pattern is possible. Our top-view
observations of impact dynamics reveal that an trapped air is responsible for
the splashing. Indeed by lowering the pressure of the surrounding air we show
that we can suppress the splashing in the explored parameter regime.Comment: 7 pages, 9 figure
How inter-firm networks influence the development of agglomerations
Non-market interactions are increasingly regarded as key explanations for spatial concentration. Consistently, both innovation and local knowledge spillovers play a central role in recent theories of agglomeration. According to these theories, exchange of localised knowledge gives firms an innovative advantage which results in better economic performance. However, it has turned out to be difficult to open the black box of economies of scale using empirical tests.\ud
Since interactions get considerable attention in recent agglomeration theory, social network methods and theory are promising approaches to research spatial agglomerations. Even more so because simultaneously, there is an increasing emphasis on interfirm ties in the network field.\ud
The goal of our research is to explore how interfirm networks influence the development of agglomerations. Firstly we provide a review on network and innovation literature in the field of spatial clusters. Secondly, we discuss measurement issues related to networks and innovation and ways to overcome them. Finally, we present preliminary results of our network study among high tech firms in the Dutch region of Twente
OH-selected AGB and post-AGB stellar objects II.Blue versus red evolution off the AGB
Using objects found in a systematic survey of the galactic Plane in the
1612-MHz OH line, we discuss in detail two ``sequences'' of post-AGB evolution,
a red and a blue. We argue that the red and the blue groups separate by initial
mass at 4Msun, based on evolutionary-sequence turn-off colours, spectral energy
distributions, outflow velocities and scaleheight. The higher-mass (blue)
objects may have earlier AGB termination. The lower-mass (red) objects undergo
very sudden reddening for IRAS colour R21\sim1.2; these sources must all
undergo a very similar process at AGB termination. The transition colour
corresponds to average initial masses of 1.7Msun. A combined IRAS-MSX colour
proves a very sensitive tool to distinguish lower-mass, early post-AGB objects
from sources still on the AGB and also to distinguish more evolved post-AGB
objects from star-forming regions. The high-mass blue objects are the likely
precursors of bipolar planetary nebulae, whereas the low-mass red objects will
evolve into elliptical planetary nebulae.Comment: 12 pages, LaTex, 7 figures (1 colour), AJ (accepted
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