130,873 research outputs found
H2 formation via the UV photo-processing of a-C:H nano-particles
Context. The photolysis of hydrogenated amorphous carbon, a-C(:H), dust by UV
photon-irradiation in the laboratory leads to the release of H2 as well as
other molecules and radicals. This same process is also likely to be important
in the interstellar medium. Aims. To investigate molecule formation arising
from the photo-dissociatively-driven, regenerative processing of a-C(:H) dust.
Methods. We explore the mechanism of a-C(:H) grain photolysis leading to the
formation of H2 and other molecules/radicals. Results. The rate constant for
the photon-driven formation of H2 from a-C(:H) grains is estimated to be
2x10^-17 cm^3 s^-1. In intense radiation fields photon-driven grain
decomposition will lead to fragmentation into daughter species rather than H2
formation. Conclusions. The cyclic re-structuring of arophatic a-C(:H)
nano-particles appears to be a viable route to formation of H2 for low to
moderate radiation field intensities (1 < G_0 < 10^2), even when the dust is
warm (T ~ 50 - 100 K).Comment: 7 pages, 2 figures, accepted for publication in A&
Evolutionary tradeoff and equilibrium in an aquatic predator-prey system
Due to the conventional distinction between ecological (rapid) and
evolutionary (slow)timescales, ecological and population models to date have
typically ignored the effects of evolution. Yet the potential for rapid
evolutionary change has been recently established and may be critical to
understanding how populations adapt to changing environments. In this paper we
examine the relationship between ecological and evolutionary dynamics, focusing
on a well-studied experimental aquatic predator-prey system (Fussmann et al.
2000; Shertzer et al. 2002; Yoshida et al. 2003). Major properties of
predator-prey cycles in this system are determined by ongoing evolutionary
dynamics in the prey population. Under some conditions, however, the
populations tend to apparently stable steady-state densities. These are the
subject of the present paper. We examine a previously developed model for the
system, to determine how evolution shapes properties of the equilibria, in
particular the number and identity of coexisting prey genotypes. We then apply
these results to explore how evolutionary dynamics can shape the responses of
the system to "management": externally imposed alterations in conditions.
Specifically, we compare the behavior of the system including evolutionary
dynamics, with predictions that would be made if the potential for rapid
evolutionary change is negelected. Finally, we posit some simple experiments to
verify our prediction that evolution can have significant qualitative effects
on observed population-level responses to changing conditions.Comment: 30 pages including 8 figures, 2 tables and an Appendix; to appear in
Bulletin of Mathematical Biology. Revised three Figures, added references and
expanded Section
Automatic assembly design project 1968/9 :|breport of economic planning committee
Investigations into automatic assembly systems have
been carried out. The conclusions show the major
features to be considered by a company operating
the machine to assemble the contact block with regard
to machine output and financial aspects.
The machine system has been shown to be economically
viable for use under suitable conditions, but the
contact block is considered to be unsuitable for
automatic assembly.
Data for machine specification, reliability and
maintenance has been provided
Random Curves by Conformal Welding
We construct a conformally invariant random family of closed curves in the
plane by welding of random homeomorphisms of the unit circle given in terms of
the exponential of Gaussian Free Field. We conjecture that our curves are
locally related to SLE for .Comment: 5 page
Self-healing fuse
Fast-acting current limiting device provides current overload protection for vulnerable circuit elements and then re-establishes conduction path within milliseconds. Fuse can also perform as fast-acting switch to clear transient circuit overloads. Fuse takes advantage of large increase in electrical resistivity that occurs when liquid metal vaporizes
Modulation of endoglin expression in islets of langerhans by VEGF reveals a novel regulator of islet endothelial cell function
BACKGROUND: Endoglin/CD105 is an auxiliary receptor for transforming growth factor-β with established roles in vascular remodelling. It has recently been shown that heterozygous endoglin deficiency in mice decreases insulin secretion in an animal model of obesity, highlighting a potential role for endoglin in the regulation of islet function. We have previously identified two different populations of endoglin expressing cells in human and mouse islets which are: (i) endothelial cells (ECs) and (ii) islet mesenchymal stromal cells. The contribution of islet EC endoglin expression to islet development and sensitivity to VEGF is unknown and is the focus of this study. RESULTS: In vitro culture of mouse islets with VEGF164 for 48 h increased endoglin mRNA levels above untreated controls but VEGF did not modulate VEGFR2, CD31 or CD34 mRNA expression or islet viability. Removal of EC-endoglin expression in vivo reduced islet EC area but had no apparent effect on islet size or architecture. CONCLUSION: EC-specific endoglin expression in islets is sensitive to VEGF and plays partial roles in driving islet vascular development, however such regulation appears to be distinct to mechanisms required to modulate islet viability and size
Bulk Viscosity in Neutron Stars from Hyperons
The contribution from hyperons to the bulk viscosity of neutron star matter
is calculated. Compared to previous works we use for the weak interaction the
one-pion exchange model rather than a current-current interaction, and include
the neutral current process. Also the sensitivity
to details of the equation of state is examined. Compared to previous works we
find that the contribution from hyperons to the bulk viscosity is about two
orders of magnitude smaller.Comment: 18 pages, to appear in Physical Review
A Wideband, Four-Element, All-Digital Beamforming System for Dense Aperture Arrays in Radio Astronomy
Densely-packed, all-digital aperture arrays form a key area of technology
development required for the Square Kilometre Array (SKA) radio telescope. The
design of real-time signal processing systems for digital aperture arrays is
currently a central challenge in pathfinder projects worldwide. We describe
interim results of such work; an heirarchical, frequency-domain beamforming
architecture for synthesising a sky beam from the wideband antenna feeds of
digital aperture arrays.Comment: 4 pages, 6 figure
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