10,887 research outputs found
Materials-Handling Hazard Controls: Assessment of Haddon’s Injury Control Strategies
This investigation assessed the applicability of Dr. William Haddon’s strategies for controlling hazards involving materials-handling operations in industrial and mining workplaces. Published over 20 years ago, Haddon’s strategies purport to include all strategies for preventing and mitigating harm to people, property, and the environment. Students in an undergraduate class were assigned to find tactical examples of each of Haddon’s strategies applicable to material handling. Haddon’s tenth strategy involving medical care and rehabilitation was not included. Their classifications were analyzed to identify points of confusion as well as points of general agreement. Students found numerous tactics for strategies involving engineering and behavioral strategies. Fewer tactics were identified for strategies involving damage control through effective and timely response
Stream network analysis and geomorphic flood plain mapping from orbital and suborbital remote sensing imagery application to flood hazard studies in central Texas
The author has identified the following significant results. Development of a quantitative hydrogeomorphic approach to flood hazard evaluation was hindered by (1) problems of resolution and definition of the morphometric parameters which have hydrologic significance, and (2) mechanical difficulties in creating the necessary volume of data for meaningful analysis. Measures of network resolution such as drainage density and basin Shreve magnitude indicated that large scale topographic maps offered greater resolution than small scale suborbital imagery and orbital imagery. The disparity in network resolution capabilities between orbital and suborbital imagery formats depends on factors such as rock type, vegetation, and land use. The problem of morphometric data analysis was approached by developing a computer-assisted method for network analysis. The system allows rapid identification of network properties which can then be related to measures of flood response
New Techniques for Relating Dynamically Close Galaxy Pairs to Merger and Accretion Rates : Application to the SSRS2 Redshift Survey
We introduce two new pair statistics, which relate close galaxy pairs to the
merger and accretion rates. We demonstrate the importance of correcting these
(and other) pair statistics for selection effects related to sample depth and
completeness. In particular, we highlight the severe bias that can result from
the use of a flux-limited survey. The first statistic, denoted N_c, gives the
number of companions per galaxy, within a specified range in absolute
magnitude. N_c is directly related to the galaxy merger rate. The second
statistic, called L_c, gives the total luminosity in companions, per galaxy.
This quantity can be used to investigate the mass accretion rate. Both N_c and
L_c are related to the galaxy correlation function and luminosity function in a
straightforward manner. We outline techniques which account for various
selection effects, and demonstrate the success of this approach using Monte
Carlo simulations. If one assumes that clustering is independent of luminosity
(which is appropriate for reasonable ranges in luminosity), then these
statistics may be applied to flux-limited surveys.
These techniques are applied to a sample of 5426 galaxies in the SSRS2
redshift survey. Using close dynamical pairs, we find N_c(-21<M_B<-18) =
0.0226+/-0.0052 and L_c(-21<M_B<-18) = 0.0216+/-0.0055 10^{10} h^2 L_sun at
z=0.015. These are the first secure estimates of low-z close pair statistics.
If N_c remains fixed with redshift, simple assumptions imply that ~ 6.6% of
present day galaxies with -21<M_B<-18 have undergone mergers since z=1. When
applied to redshift surveys of more distant galaxies, these techniques will
yield the first robust estimates of evolution in the galaxy merger and
accretion rates. [Abridged]Comment: 26 pages (including 10 postscript figures) plus 3 gif figures.
Accepted for publication in ApJ. Paper (including full resolution images)
also available at http://www.astro.utoronto.ca/~patton/ssrs2, along with
associated pair classification experiment (clickable version of Figure 5
A Hubble Space Telescope Snapshot Survey of Dynamically Close Galaxy Pairs in the CNOC2 Redshift Survey
We compare the structural properties of two classes of galaxies at
intermediate redshift: those in dynamically close galaxy pairs, and those which
are isolated. Both samples are selected from the CNOC2 Redshift Survey, and
have redshifts in the range 0.1 < z <0.6. Hubble Space Telescope WFPC2 images
were acquired as part of a snapshot survey, and were used to measure bulge
fraction and asymmetry for these galaxies. We find that paired and isolated
galaxies have identical distributions of bulge fractions. Conversely, we find
that paired galaxies are much more likely to be asymmetric (R_T+R_A >= 0.13)
than isolated galaxies. Assuming that half of these pairs are unlikely to be
close enough to merge, we estimate that 40% +/- 11% of merging galaxies are
asymmetric, compared with 9% +/- 3% of isolated galaxies. The difference is
even more striking for strongly asymmetric (R_T+R_A >= 0.16) galaxies: 25% +/-
8% for merging galaxies versus 1% +/- 1% for isolated galaxies. We find that
strongly asymmetric paired galaxies are very blue, with rest-frame B-R colors
close to 0.80, compared with a mean (B-R)_0 of 1.24 for all paired galaxies. In
addition, asymmetric galaxies in pairs have strong [OII]3727 emission lines. We
conclude that close to half of the galaxy pairs in our sample are in the
process of merging, and that most of these mergers are accompanied by triggered
star formation.Comment: Accepted for publication in the Astronomical Journal. 40 pages,
including 15 figures. For full resolution version, please see
http://www.trentu.ca/physics/dpatton/hstpairs
Long-lived heteronuclear spin-singlet states
We report observation of long-lived spin-singlet states in a 13C-1H spin pair
at zero magnetic field. In 13C-labeled formic acid, we observe spin-singlet
lifetimes as long as 37 seconds, about a factor of three longer than the T1
lifetime of dipole polarization in the triplet state. We also observe that the
lifetime of the singlet-triplet coherence, T2, is longer than T1. Moreover, we
demonstrate that this singlet states formed by spins of a heteronucleus and a
1H nucleus, can exhibit longer lifetimes than the respective triplet states in
systems consisting of more than two nuclear spins. Although long-lived
homonuclear spin-singlet states have been extensively studied, this is the
first experimental observation of analogous spin-singlets consisting of a
heteronucleus and a proton.Comment: 5 pages, 4 figure
Swimming is never without risk: opening up on learning through activism and research
This article examines my own becoming as Elisabeth and as a researcher. It is about working as a support worker, coaching teams that are trying to realize inclusive education for a child, and my PhD process, which relies on these practices. My intention here is to unfold several aspects, blockages, possibilities, and tensions that can make sense of my messy struggle. The never-ending learning through working with people, listening to their stories, and taking responsibility are important ingredients of my engagement. It is necessary to provide insights and justify my multiple positions to avoid falling into a narcissistic trap. In doing so, I will seek help from Levinas and in concepts of Deleuze and Guattari to (re-)construct my own understanding
The Millennium Galaxy Catalogue: The connection between close pairs and asymmetry; implications for the galaxy merger rate
We compare the use of galaxy asymmetry and pair proximity for measuring
galaxy merger fractions and rates for a volume limited sample of 3184 galaxies
with -21 < M(B) -5 log h < -18 mag. and 0.010 < z < 0.123 drawn from the
Millennium Galaxy Catalogue. Our findings are that:
(i) Galaxies in close pairs are generally more asymmetric than isolated
galaxies and the degree of asymmetry increases for closer pairs. At least 35%
of close pairs (with projected separation of less than 20 h^{-1} kpc and
velocity difference of less than 500 km s^{-1}) show significant asymmetry and
are therefore likely to be physically bound.
(ii) Among asymmetric galaxies, we find that at least 80% are either
interacting systems or merger remnants. However, a significant fraction of
galaxies initially identified as asymmetric are contaminated by nearby stars or
are fragmented by the source extraction algorithm. Merger rates calculated via
asymmetry indices need careful attention in order to remove the above sources
of contamination, but are very reliable once this is carried out.
(iii) Close pairs and asymmetries represent two complementary methods of
measuring the merger rate. Galaxies in close pairs identify future mergers,
occurring within the dynamical friction timescale, while asymmetries are
sensitive to the immediate pre-merger phase and identify remnants.
(iv) The merger fraction derived via the close pair fraction and asymmetries
is about 2% for a merger rate of (5.2 +- 1.0) 10^{-4} h^3 Mpc^{-3} Gyr^{-1}.
These results are marginally consistent with theoretical simulations (depending
on the merger time-scale), but imply a flat evolution of the merger rate with
redshift up to z ~1.Comment: 10 pages, 10 figures, emulateapj format. ApJ, accepte
Self-Referential Noise and the Synthesis of Three-Dimensional Space
Generalising results from Godel and Chaitin in mathematics suggests that
self-referential systems contain intrinsic randomness. We argue that this is
relevant to modelling the universe and show how three-dimensional space may
arise from a non-geometric order-disorder model driven by self-referential
noise.Comment: Figure labels correcte
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