27,315 research outputs found
Cosmological Parameters from the Comparison of the 2MASS Gravity Field with Peculiar Velocity Surveys
We compare the peculiar velocity field within 65 Mpc predicted from
2MASS photometry and public redshift data to three independent peculiar
velocity surveys based on type Ia supernovae, surface brightness fluctuations
in ellipticals, and Tully-Fisher distances to spirals. The three peculiar
velocity samples are each in good agreement with the predicted velocities and
produce consistent results for \beta_{K}=\Omega\sbr{m}^{0.6}/b_{K}. Taken
together the best fit . We explore the effects of
morphology on the determination of by splitting the 2MASS sample into
E+S0 and S+Irr density fields and find both samples are equally good tracers of
the underlying dark matter distribution, but that early-types are more
clustered by a relative factor b\sbr{E}/b\sbr{S} \sim 1.6. The density
fluctuations of 2MASS galaxies in Mpc spheres in the local volume is
found to be \sigma\sbr{8,K} = 0.9. From this result and our value of
, we find \sigma_8 (\Omega\sbr{m}/0.3)^{0.6} = 0.91\pm0.12. This
is in excellent agreement with results from the IRAS redshift surveys, as well
as other cosmological probes. Combining the 2MASS and IRAS peculiar velocity
results yields \sigma_8 (\Omega\sbr{m}^/0.3)^{0.6} = 0.85\pm0.05.Comment: 11 pages, ApJ accepte
Aspects of fracture mechanics in cryogenic model design. Part 1: Fundamentals of fracture mechanics
The use of fracture mechanics for predicting fracture and fatigue crack growth in metals is presented
A Test for Large-Scale Systematic Errors in Maps of Galactic Reddening
Accurate maps of Galactic reddening are important for a number of
applications, such as mapping the peculiar velocity field in the nearby
Universe. Of particular concern are systematic errors which vary slowly as a
function of position on the sky, as these would induce spurious bulk flow. We
have compared the reddenings of Burstein & Heiles (BH) and those of Schlegel,
Finkbeiner & Davis (SFD) to independent estimates of the reddening, for
Galactic latitudes |b| > 10. Our primary source of Galactic reddening estimates
comes from comparing the difference between the observed B-V colors of
early-type galaxies, and the predicted B-V color determined from the B-V--Mg_2
relation. We have fitted a dipole to the residuals in order to look for
large-scale systematic deviations. There is marginal evidence for a dipolar
residual in the comparison between the SFD maps and the observed early-type
galaxy reddenings. If this is due to an error in the SFD maps, then it can be
corrected with a small (13%) multiplicative dipole term. We argue, however,
that this difference is more likely to be due to a small (0.01 mag.) systematic
error in the measured B-V colors of the early-type galaxies. This
interpretation is supported by a smaller, independent data set (globular
cluster and RR Lyrae stars), which yields a result inconsistent with the
early-type galaxy residual dipole. BH reddenings are found to have no
significant systematic residuals, apart from the known problem in the region
230 < l < 310, -20 < b < 20.Comment: 8 pages, PASP, in press (Jan 1999
Changing perceptions of preservice teachers : innovations in middle schooling teacher education
For the past twenty years, the disengagement of early adolescents has been the focus of much of the literature related to middle schooling. In response, some universities in Australia have introduced teacher education programs that focus upon graduating specialised middle schooling teachers. Constructing such programs is at the centre of much debate and discussion, however, it is advocated that positive futures for early adolescents can be enhanced through quality middle schooling teacher education programs (Education Queensland, 2004). At a Queensland university campus, middle schooling elective units were introduced as part of the Bachelor of Education (primary) degree. The design of the units was to support preservice teachers to gain the theoretical and pedagogical knowledge to engage and promote early adolescent learning. An innovative approach to the delivery of the units was promoted by a partnership agreement between local schools and the campus. The partnership allowed preservice teachers to combine university classes with opportunities to visit exemplary classrooms to observe, participate and reflect upon middle school teaching practices. The aim of this study was to explore and describe the 38 first-year preservice teachersâ perceptions of their first middle schooling elective unit and to ascertain whether the combination of university classes and school-based experiences assisted their development of middle schooling concepts and approaches. Data were gathered using pre-test and post-test questionnaires combined with guided written reflections to record their views before, after and during the unit delivery. Results indicated that initially 34 preservice teachers had little understanding of middle schooling concepts and pedagogical practices, however, 11 participants recognised that bullying and peer pressure were issues experienced by early adolescents. The collation of the written reflections supported the combined delivery of the middle years unit further supporting the inclusion of school experiences with university delivered units
The Peculiar Velocities of Local Type Ia Supernovae and their Impact on Cosmology
We quantify the effect of supernova Type Ia peculiar velocities on the
derivation of cosmological parameters. The published distant and local Ia SNe
used for the Supernova Legacy Survey first-year cosmology report form the
sample for this study. While previous work has assumed that the local SNe are
at rest in the CMB frame (the No Flow assumption), we test this assumption by
applying peculiar velocity corrections to the local SNe using three different
flow models. The models are based on the IRAS PSCz galaxy redshift survey, have
varying beta = Omega_m^0.6/b, and reproduce the Local Group motion in the CMB
frame. These datasets are then fit for w, Omega_m, and Omega_Lambda using
flatness or LambdaCDM and a BAO prior. The chi^2 statistic is used to examine
the effect of the velocity corrections on the quality of the fits. The most
favored model is the beta=0.5 model, which produces a fit significantly better
than the No Flow assumption, consistent with previous peculiar velocity
studies. By comparing the No Flow assumption with the favored models we derive
the largest potential systematic error in w caused by ignoring peculiar
velocities to be Delta w = +0.04. For Omega_Lambda, the potential error is
Delta Omega_Lambda = -0.04 and for Omega_m, the potential error is Delta
Omega_m < +0.01. The favored flow model (beta=0.5) produces the following
cosmological parameters: w = -1.08 (+0.09,-0.08), Omega_m = 0.27 (+0.02,-0.02)
assuming a flat cosmology, and Omega_Lambda = 0.80 (+0.08,-0.07) and Omega_m =
0.27 (+0.02,-0.02) for a w = -1 (LambdaCDM) cosmology.Comment: 4 pages, 2 figures, 1 table, accepted for publication in ApJ Letter
A study of fatigue and fracture in 7075-T6 aluminum alloy in vacuum and air environments
Axial load fatigue life, fatigue-crack propagation, and fracture toughness experiments were conducted on sheet specimens made of 7075-T6 aluminum alloy. These experiments were conducted at pressures ranging from atmospheric to 5 x 10 to the minus 8th torr. Analysis of the results from the fatigue life experiments indicated that for a given stress level, lower air pressures produced longer fatigue lives. At a pressure of 5 x 10 to the minus 8th torr fatigue lives were 15 or more times as long as at atmospheric pressure. Analysis of the results from the fatigue crack propagation experiments indicated that for small stress intensity factor ranges the fatigue crack propagation rates were up to twice as high at atmospheric pressure as in vacuum. The fracture toughness of 7075-T6 was unaffected by the vacuum environment. Fractographic examination showed that specimens tested in both vacuum and air developed fatigue striations. Considerably more striations developed on specimens tested at atmospheric pressure, however
Investigation of fatigue crack growth in Ti- 8Al-1Mo-1V /duplex-annealed/ specimens having various widths
Axial-load fatigue crack propagation tests on duplex annealed titanium alloy specimens having various width
Missing Women and Bare Branches: Gender Balance and Conflict
The emerging subfield of âsecurity demographicsâ examines the linkages between population dynamics and the security trajectories of nation-states. For the last 5 to 10 years, researchers have examined the security aspects of such topics as the demographic transition, the sub-replacement birth rates of developed economies, the proportion of young men as compared to older men in the population, the effects of legal and illegal immigration, and the effects of pandemics such as AIDS and drug-resistant tuberculosis.
This paper aims to add the variable of gender balance to the discussion: are societies with an abnormal ratio between men and women less secure
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