63,033 research outputs found
Pretreatment method for anti-wettable materials
Anti-wettable materials brazing processes using titanium and zirconium for surface pretreatmen
The quiescent progenitors of four Type II-P/L supernovae
We present Large Binocular Telescope difference imaging data for the final
years of four Type II-P/L supernovae progenitors. For all four, we find no
significant evidence for stochastic or steady variability in the U, B, V, or
R-bands. Our limits constrain variability to no more than roughly 5-10% of the
expected R-band luminosities of the progenitors. These limits are comparable to
the observed variability of red supergiants in the Magellanic Clouds. Based on
these four events, the probability of a Type II-P/L progenitor having an
extended outburst after Oxygen ignition is <37% at 90% confidence. Our
observations cannot exclude short outbursts in which the progenitor returns to
within ~10% of its quiescent flux on the time scale of months with no dust
formation.Comment: 9 pages, 8 figures, 1 table. Accepted to MNRA
Carbon Trading with Blockchain
Blockchain has the potential to accelerate the deployment of emissions
trading systems (ETS) worldwide and improve upon the efficiency of existing
systems. In this paper, we present a model for a permissioned blockchain
implementation based on the successful European Union (EU) ETS and discuss its
potential advantages over existing technology. We propose an ETS model that is
both backwards compatible and future-proof, characterised by
interconnectedness, transparency, tamper-resistance and high liquidity.
Further, we identify key challenges to implementation of a blockchain ETS, as
well as areas of future work required to enable a fully-decentralised
blockchain ETS
Relativistic Effects in Extrasolar Planetary Systems
This paper considers general relativistic (GR) effects in currently observed
extrasolar planetary systems. Although GR corrections are small, they can
compete with secular interactions in these systems and thereby play an
important role. Specifically, some of the observed multiple planet systems are
close to secular resonance, where the dynamics is extremely sensitive to GR
corrections, and these systems can be used as laboratories to test general
relativity. For the three-planet solar system Upsilon Andromedae, secular
interaction theory implies an 80% probability of finding the system with its
observed orbital elements if GR is correct, compared with only a 2% probability
in the absence of GR. In the future, tighter constraints can be obtained with
increased temporal coverage.Comment: Accepted for publication in International Journal of Modern Physics
D; this paper received ``Honorable Mention'' in the 2006 Essay Competition of
the Gravity Research Foundation; 9 pages including 1 figur
Stellar Mergers Are Common
The observed Galactic rate of stellar mergers or the initiation of common
envelope phases brighter than M_V=-3 (M_I=-4) is of order 0.5 (0.3)/year with
90% confidence statistical uncertainties of 0.24-1.1 (0.14-0.65) and factor of
2 systematic uncertainties. The (peak) luminosity function is roughly dN/dL
L^(-1.4+/-0.3), so the rates for events more luminous than V1309 Sco (M_V=-7
mag) or V838Mon (M_V=-10 mag) are lower at r~0.1/year and 0.03/year,
respectively. The peak luminosity is a steep function of progenitor mass, L
M^(2-3). This very roughly parallels the scaling of luminosity with mass on the
main sequence, but the transients are ~2000-4000 times more luminous at peak.
Combining these, the mass function of the progenitors, dN/dM M^(-2.0+/-0.8), is
consistent with the initial mass function, albeit with broad uncertainties.
These observational results are also broadly consistent with the estimates of
binary population synthesis models. While extragalactic variability surveys can
better define the rates and properties of the high luminosity events,
systematic, moderate depth (I>16 mag) surveys of the Galactic plane are needed
to characterize the low luminosity events. The existing Galactic samples are
only ~20% complete and Galactic surveys are (at best) reaching a typical
magnitude limit of <13 mag.Comment: Submitted to MNRAS (13 pages, 6 figures, 3 tables
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