2,359 research outputs found
Problems in property valuation (Lowell, Massachusetts)
Thesis (M.B.A.)--Boston University, 1935. This item was digitized by the Internet Archive
Photoionisation and Heating of a Supernova Driven, Turbulent, Interstellar Medium
The Diffuse Ionised Gas (DIG) in galaxies traces photoionisation feedback
from massive stars. Through three dimensional photoionisation simulations, we
study the propagation of ionising photons, photoionisation heating and the
resulting distribution of ionised and neutral gas within snapshots of
magnetohydrodynamic simulations of a supernova driven turbulent interstellar
medium. We also investigate the impact of non-photoionisation heating on
observed optical emission line ratios. Inclusion of a heating term which scales
less steeply with electron density than photoionisation is required to produce
diagnostic emission line ratios similar to those observed with the Wisconsin
H{\alpha} Mapper. Once such heating terms have been included, we are also able
to produce temperatures similar to those inferred from observations of the DIG,
with temperatures increasing to above 15000 K at heights |z| > 1 kpc. We find
that ionising photons travel through low density regions close to the midplane
of the simulations, while travelling through diffuse low density regions at
large heights. The majority of photons travel small distances (< 100pc);
however some travel kiloparsecs and ionise the DIG.Comment: 10 pages, 13 figures, accepted to MNRA
Early Results from the Wisconsin H-Alpha Mapper Southern Sky Survey
After a successful eleven-year campaign at Kitt Peak, we moved the Wisconsin
H-Alpha Mapper (WHAM) to Cerro Tololo in early 2009. Here we present some of
the early data after a few months under southern skies. These maps begin to
complete the first all-sky, kinematic survey of the diffuse H-alpha emission
from the Milky Way. Much of this emission arises from the Warm Ionized Medium
(WIM), a significant component of the ISM that extends a few kiloparsecs above
the Galactic disk. While this first look at the data focuses on the H-alpha
survey, WHAM is also capable of observing many other optical emission lines,
revealing fascinating trends in the temperature and ionization state of the
WIM. Our ongoing studies of the physical conditions of diffuse ionized gas will
continue from the southern hemisphere following the H-alpha survey. In
addition, future observations will cover the full velocity range of the
Magellanic Stream, Bridge, and Clouds to trace the ionized gas associated with
these neighboring systems.Comment: 4 pages, 2 figures. To appear in "The Dynamic ISM: A celebration of
the Canadian Galactic Plane Survey," ASP Conference Serie
Prospective relationships between body weight and physical activity: an observational analysis from the NAVIGATOR study
Objectives: While bidirectional relationships exist between body weight and physical activity, direction of causality remains uncertain and previous studies have been limited by self-reported activity or weight and small sample size. We investigated the prospective relationships between weight and physical activity.
Design: Observational analysis of data from the Nateglinide And Valsartan in Impaired Glucose Tolerance Outcomes Research (NAVIGATOR) study, a double-blinded randomised clinical trial of nateglinide and valsartan, respectively.
Setting Multinational study of 9306 participants.
Participants: Participants with biochemically confirmed impaired glucose tolerance had annual measurements of both weight and step count using research grade pedometers, worn for 7 days consecutively. Along with randomisation to valsartan or placebo plus nateglinide or placebo, participants took part in a lifestyle modification programme.
Outcome measures: Longitudinal regression using weight as response value and physical activity as predictor value was conducted, adjusted for baseline covariates. Analysis was then repeated with physical activity as response value and weight as predictor value. Only participants with a response value preceded by at least three annual response values were included.
Results: Adequate data were available for 2811 (30%) of NAVIGATOR participants. Previous weight (χ2=16.8; p<0.0001), but not change in weight (χ2=0.1; p=0.71) was inversely associated with subsequent step count, indicating lower subsequent levels of physical activity in heavier individuals. Change in step count (χ2=5.9; p=0.02) but not previous step count (χ2=0.9; p=0.34) was inversely associated with subsequent weight. However, in the context of trajectories already established for weight (χ2 for previous weight measurements 747.3; p<0.0001) and physical activity (χ2 for previous step count 432.6; p<0.0001), these effects were of limited clinical importance.
Conclusions: While a prospective bidirectional relationship was observed between weight and physical activity, the magnitude of any effect was very small in the context of natural trajectories already established for these variables
Concurrentie en externe effecten
In tegenstelling tot wat De Man aan het begin van zijn reactie stelt, hielden wij in ons artikel 'Handen af van ECT?' géén pleidooi voor
het handhaven van de monopoliepositie van ECT in de Rotterdamse haven. Ons gaat het om het dilemma tussen nationaal en Europees
beleid gericht op het zoveel mogelijk bevorderen van concurrentie en de wenselijkheid om zoveel mogelijk rekening te houden met de
externe effecten van concurrentie (zoals milieu en technologische ontwikkeling
Densities and filling factors of the DIG in the Solar neighbourhood
For the first time we have combined dispersion measures and emission measures
towards 38 pulsars at KNOWN distances from which we derived the mean electron
density in clouds, N_c, and their volume filling factor, F_v, averaged along
the line of sight. The emission measures were corrected for absorption by dust
and contributions from beyond the pulsar distance. Results: The scale height of
the electron layer for our sample is 0.93+/-0.13 kpc and the midplane electron
density is 0.023+/-0.004 cm^-3, in agreement with earlier results. The average
density along the line of sight is = 0.018+/-0.002 cm^-3 and nearly
constant. Since = F_v N_c, an inverse relationship between F_v and N_c is
expected. We find F_v(N_c) = (0.011+/-0.003) N_c^{-1.20+/-0.13}, which holds
for the ranges N_c = 0.05-1 cm^-3 and F_v = 0.4-0.01. Near the Galactic plane
the dependence of F_v on N_c is significantly stronger than away from the
plane. F_v does not systematically change along or perpendicular to the
Galactic plane, but the spread about the mean value of 0.08+/-0.02 is
considerable. Conclusions: The inverse F_v-N_c relation is consistent with a
hierarchical, fractal density distribution in the diffuse ionized gas (DIG)
caused by turbulence. The observed near constancy of then is a signature
of fractal structure in the ionized medium, which is most pronounced outside
the thin disk.Comment: 9 pages, 9 figures. Accepted for publication in A&
Determination of the Far-Infrared Cosmic Background Using COBE/DIRBE and WHAM Data
Determination of the cosmic infrared background (CIB) at far infrared
wavelengths using COBE/DIRBE data is limited by the accuracy to which
foreground interplanetary and Galactic dust emission can be modeled and
subtracted. Previous determinations of the far infrared CIB (e.g., Hauser et
al. 1998) were based on the detection of residual isotropic emission in skymaps
from which the emission from interplanetary dust and the neutral interstellar
medium were removed. In this paper we use the Wisconsin H-alpha Mapper (WHAM)
Northern Sky Survey as a tracer of the ionized medium to examine the effect of
this foreground component on determination of the CIB. We decompose the DIRBE
far infrared data for five high Galactic latitude regions into H I and H-alpha
correlated components and a residual component. We find the H-alpha correlated
component to be consistent with zero for each region, and we find that addition
of an H-alpha correlated component in modeling the foreground emission has
negligible effect on derived CIB results. Our CIB detections and 2 sigma upper
limits are essentially the same as those derived by Hauser et al. and are given
by nu I_nu (nW m-2 sr-1) < 75, < 32, 25 +- 8, and 13 +- 3 at 60, 100, 140, and
240 microns, respectively. Our residuals have not been subjected to a detailed
anisotropy test, so our CIB results do not supersede those of Hauser et al. We
derive upper limits on the 100 micron emissivity of the ionized medium that are
typically about 40% of the 100 micron emissivity of the neutral atomic medium.
This low value may be caused in part by a lower dust-to-gas mass ratio in the
ionized medium than in the neutral medium, and in part by a shortcoming of
using H-alpha intensity as a tracer of far infrared emission.Comment: 38 pages, 8 figures. Accepted for publication in Ap
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