13,561 research outputs found
Hands-on Gravitational Wave Astronomy: Extracting astrophysical information from simulated signals
In this paper we introduce a hands-on activity in which introductory
astronomy students act as gravitational wave astronomers by extracting
information from simulated gravitational wave signals. The process mimics the
way true gravitational wave analysis will be handled by using plots of a pure
gravitational wave signal. The students directly measure the properties of the
simulated signal, and use these measurements to evaluate standard formulae for
astrophysical source parameters. An exercise based on the discussion in this
paper has been written and made publicly available online for use in
introductory laboratory courses.Comment: 5 pages, 4 figures; submitted to Am. J. Phy
Science Icebreaker Activities: An Example from Gravitational Wave Astronomy
At the beginning of a class or meeting an icebreaker activity is often used
to help loosen the group and get everyone talking. Our motivation is to develop
activities that serve the purpose of an icebreaker, but are designed to enhance
and supplement a science-oriented agenda. The subject of this article is an
icebreaker activity related to gravitational wave astronomy. We first describe
the unique gravitational wave signals from three distinct sources:
monochromatic binaries, merging compact objects, and extreme mass ratio
encounters. These signals form the basis of the activity where participants
work to match an ideal gravitational wave signal with noisy detector output for
each type of source.Comment: Accepted to The Physics Teacher. Original manuscript divided into two
papers at the request of the referee. For a related paper on gravitational
wave observatories see physics/050920
The star formation histories of early-type galaxies: insights from the rest-frame ultra-violet
Our current understanding of the star formation histories of early-type
galaxies is reviewed, in the context of recent observational studies of their
ultra-violet (UV) properties. Combination of UV and optical spectro-photometric
data indicates that the bulk of the stellar mass in the early-type population
forms at high redshift (z > 2), typically over short timescales (< 1 Gyr).
Nevertheless, early-types of all luminosities form stars over the lifetime of
the Universe, with most luminous (-23 < M(V) < -21) systems forming 10-15% of
their stellar mass after z = 1 (with a scatter to higher value), while their
less luminous (M(V) > -21) counterparts form 30-60% of their mass in the same
redshift range. The large scatter in the (rest-frame) UV colours in the
redshift range 0 < z < 0.7 indicates widespread low-level star formation in the
early-type population over the last 8 billion years. The mass fraction of young
(< 1 Gyr old) stars in luminous early-type galaxies varies between 1% and 6% at
z~0 and is in the range 5-13% at z~0.7. The intensity of recent star formation
and the bulk of the UV colour distribution is consistent with what might be
expected from minor mergers (mass ratios < 1:6) in an LCDM cosmology.Comment: Brief Review, Mod. Phys. Lett.
Long-Term Dynamics of Leafy Spurge (\u3ci\u3eEuphorbia esula\u3c/i\u3e) and its Biocontrol Agent, Flea Beetles in the Genus Aphthona
Three flea beetle species (Aphthona spp.), first introduced into North America in 1988, have come to be regarded as effective biological control organisms for leafy spurge (Euphorbia esula). The black flea beetles (Aphthona lacertosa and A. czwalinae) in particular have been shown to cause reductions in leafy spurge stem counts in the northern Great Plains, while the brown flea beetle (A. nigriscutis) has persisted and spread, but has not been found to be as effective at controlling leafy spurge. The ability of black flea beetles to control leafy spurge in any given year, however, has been found to vary. To better understand the long-term effects of flea beetle herbivory on leafy spurge, we monitored stem counts of leafy spurge and numbers of black and brown flea beetles at three sites on two National Wildlife Refuges in east-central North Dakota, USA, from 1998 to 2006. Brown flea beetle numbers were observed to be negligible on these sites. Over the 9 years of the study, black flea beetles were seen to spread over the three study sites and leafy spurge stem counts declined substantially on two of the three sites. Even at low densities of spurge, black flea beetle populations persisted, a necessary prerequisite for long-term control. We used structural equation models (SEM) to assess the yearly effects of black flea beetles, soil texture, and refuge site on leafy spurge stem counts over this time period. We then used equations developed from the SEM analysis to explore flea beetle–leafy spurge dynamics over time, after controlling for soil texture and refuge. Yearly effect strength of black flea beetles on leafy spurge was found to be modest, largely owing to substantial spatial variability in control. However, simulation results based on prediction coefficients revealed leafy spurge to be highly responsive to increases in flea beetle populations on average
CLEF 2017 NewsREEL Overview: Offline and Online Evaluation of Stream-based News Recommender Systems
The CLEF NewsREEL challenge allows researchers to evaluate news
recommendation algorithms both online (NewsREEL Live) and offline (News-
REEL Replay). Compared with the previous year NewsREEL challenged participants
with a higher volume of messages and new news portals. In the 2017
edition of the CLEF NewsREEL challenge a wide variety of new approaches have
been implemented ranging from the use of existing machine learning frameworks,
to ensemble methods to the use of deep neural networks. This paper gives an
overview over the implemented approaches and discusses the evaluation results.
In addition, the main results of Living Lab and the Replay task are explained
Prospects for observing ultra-compact binaries with space-based gravitational wave interferometers and optical telescopes
Space-based gravitational wave interferometers are sensitive to the galactic
population of ultra-compact binaries. An important subset of the ultra-compact
binary population are those stars that can be individually resolved by both
gravitational wave interferometers and electromagnetic telescopes. The aim of
this paper is to quantify the multi-messenger potential of space-based
interferometers with arm-lengths between 1 and 5 Gm. The Fisher Information
Matrix is used to estimate the number of binaries from a model of the Milky Way
which are localized on the sky by the gravitational wave detector to within 1
and 10 square degrees and bright enough to be detected by a magnitude limited
survey. We find, depending on the choice of GW detector characteristics,
limiting magnitude, and observing strategy, that up to several hundred
gravitational wave sources could be detected in electromagnetic follow-up
observations.Comment: 6 pages, 3 figures Updated to include new results. Submitted to MNRA
Flows, Fragmentation, and Star Formation. I. Low-mass Stars in Taurus
The remarkably filamentary spatial distribution of young stars in the Taurus
molecular cloud has significant implications for understanding low-mass star
formation in relatively quiescent conditions. The large scale and regular
spacing of the filaments suggests that small-scale turbulence is of limited
importance, which could be consistent with driving on large scales by flows
which produced the cloud. The small spatial dispersion of stars from gaseous
filaments indicates that the low-mass stars are generally born with small
velocity dispersions relative to their natal gas, of order the sound speed or
less. The spatial distribution of the stars exhibits a mean separation of about
0.25 pc, comparable to the estimated Jeans length in the densest gaseous
filaments, and is consistent with roughly uniform density along the filaments.
The efficiency of star formation in filaments is much higher than elsewhere,
with an associated higher frequency of protostars and accreting T Tauri stars.
The protostellar cores generally are aligned with the filaments, suggesting
that they are produced by gravitational fragmentation, resulting in initially
quasi-prolate cores. Given the absence of massive stars which could strongly
dominate cloud dynamics, Taurus provides important tests of theories of
dispersed low-mass star formation and numerical simulations of molecular cloud
structure and evolution.Comment: 32 pages, 9 figures: to appear in Ap
Turbulent Cooling Flows in Molecular Clouds
We propose that inward, subsonic flows arise from the local dissipation of
turbulent motions in molecular clouds. Such "turbulent cooling flows" may
account for recent observations of spatially extended inward motions towards
dense cores. These pressure-driven flows may arise from various types of
turbulence and dissipation mechanisms. For the example of MHD waves and
turbulence damped by ion-neutral friction, sustained cooling flow requires that
the outer gas be sufficiently turbulent, that the inner gas have marginal
field-neutral coupling, and that this coupling decrease sufficiently rapidly
with increasing density. These conditions are most likely met at the transition
between outer regions ionized primarily by UV photons and inner regions ionized
primarily by cosmic rays. If so, turbulent cooling flows can help form dense
cores, with speeds faster than expected for ambipolar diffusion. Such motions
could reduce the time needed for dense core formation and could precede and
enhance the motions of star-forming gravitational infall.Comment: To appear ApJL, Nov.10, 4 ApJ style pages, Postscrip
A Dynamical Study of the Non-Star Forming Translucent Molecular Cloud MBM16: Evidence for Shear Driven Turbulence in the Interstellar Medium
We present the results of a velocity correlation study of the high latitude
cloud MBM16 using a fully sampled CO map, supplemented by new CO
data. We find a correlation length of 0.4 pc. This is similar in size to the
formaldehyde clumps described in our previous study. We associate this
correlated motion with coherent structures within the turbulent flow. Such
structures are generated by free shear flows. Their presence in this non-star
forming cloud indicates that kinetic energy is being supplied to the internal
turbulence by an external shear flow. Such large scale driving over long times
is a possible solution to the dissipation problem for molecular cloud
turbulence.Comment: Uses AAS aasms4.sty macros. Accepted for publication in Ap
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