824 research outputs found
Decoupling the Role of Inertia and Gravity on Particle Dispersion
Turbulent gas flows laden with small, dense particles are encountered in a wide number of important applications in both industrial settings and aerodynamics applications. Particle interactions with the underlying turbulent flow are exceedingly complex and, consequently, difficult to accurately model. The difficulty arises primarily due to the fact that response of a particle to the local environment is dictated by turbulence properties in the reference frame moving with the particle (particle-Lagrangian). The particle-Lagrangian reference frame is in turn dependent upon the particle relaxation time (time constant) as well as gravitational drift. The combination of inertial and gravitational effects in this frame complicates our ability to accurately predict particle-laden flows since measurements in the particle-Lagrangian reference frame are difficult to obtain. Therefore, in this work we will examine separately the effects of inertia and gravitational drift on particle dispersion through a combination of physical and numerical experiments. In this study, particle-Lagrangian measurements will be obtained in physical experiments using stereo image velocimetry. Gravitational drift will be varied in the variable-g environments of the NASA DC-9 and in the zero-g environment at the drop tower at NASA-Lewis. Direct numerical simulations will be used to corroborate the measurements from the variable-g experiments. We expect that this work will generate new insight into the underlying physics of particle dispersion and will, in turn, lead to more accurate models of particle transport in turbulent flows
Galaxy Groups Associated with Gravitational Lenses and H_0 from B1608+656
Compact groups of galaxies recently have been discovered in association with
several strong gravitational lens systems. These groups provide additional
convergence to the lensing potential and thus affect the value of H_0 derived
from the systems. Lens system time delays are now being measured with
uncertainties of only a few percent or better. Additionally, vast improvements
are being made in incorporating observational constraints such as Einstein ring
structures and stellar velocity dispersions into the lens models. These
advances are reducing the uncertainties on H_0 to levels at which the the
effects of associated galaxy groups may contribute significantly to the overall
error budget. We describe a dedicated multiwavelength program, using Keck, HST,
and Chandra, to find such groups and measure their properties. We present, as a
case study, results obtained from observations of the CLASS lens system
B1608+656 and discuss the implications for the value of H_0 derived from this
system.Comment: To appear in Proceedings of IAU Symposium 225: Impact of
Gravitational Lensing on Cosmology, 6 pages, 2 figure
Deep Imaging of AXJ2019+112: The Luminosity of a ``Dark Cluster''
We detect a distant cluster of galaxies centered on the QSO lens and luminous
X-ray source AXJ2019+112, a.k.a. ``The Dark Cluster'' (Hattori et al 1997).
Using deep V,I Keck images and wide-field K_s imaging from the NTT, a tight red
sequence of galaxies is identified within a radius of 0.2 h^{-1} Mpc of the
known z=1.01 elliptical lensing galaxy. The sequence, which includes the
central elliptical galaxy, has a slope in good agreement with the model
predictions of Kodama et al (1998) for z~1. We estimate the integrated
rest-frame luminosity of the cluster to be L_V > 3.2 x 10^{11}h^{-2}L_{\sun}
(after accounting for significant extinction at the low latitude of this
field), more than an order of magnitude higher than previous estimates. The
central region of the cluster is deconvolved using the technique of Magain,
Courbin & Sohy (1998), revealing a thick central arc coincident with an
extended radio source. All the observed lensing features are readily explained
by differential magnification of a radio loud AGN by a shallow elliptical
potential. The QSO must lie just outside the diamond caustic, producing two
images, and the arc is a highly magnified image formed from a region close to
the center of the host galaxy, projecting inside the caustic. The
mass--to--light ratio within an aperture of 0.4 h ^{-1} Mpc is M_x/L_V=
224^{+112}_{-78}h(M/L_V)_{\sun}, using the X-ray temperature. The strong lens
model yields a compatible value, M/L_V= 372^{+94}_{-94}h(M/L_V)_{\sun}, whereas
an independent weak lensing analysis sets an upper limit of M/L_V <520
h(M/L_V)_{\sun}, typical of massive clusters.Comment: AAS Latex format, 24 pages, 9 figures. Fig 1a,b available at
http://astro.berkeley.edu/~benitezn/cluster.html . Submitted to ApJ on August
15t
Deriving Historical Temperature and Precipitation Time Series For Alaska Climate Divisions Via Climatologically Aided Interpolation
This paper describes the construction of temperature and precipitation time series for climate divisions in Alaska for 1925-2015. Designed for NOAA climate monitoring applications, these new series build upon the divisional data of Bieniek et al. (2014) through the inclusion of additional observing stations, temperature bias adjustments, supplemental temperature elements, and enhanced computational techniques (i.e., climatologically aided interpolation). The new NOAA series are in general agreement with Bieniek et al. (2014), differences being attributable to the underlying methods used to compute divisional averages in each dataset. Trends in minimum temperature are significant in most divisions whereas trends in maximum temperature are generally not significant in the eastern third of the state. Likewise, the statewide rate of warming in minimum temperature (0.158°C dec-1) is roughly 50% larger than that of maximum temperature (0.101 °C dec-1). Trends in precipitation are not significant for most divisions or for the state as a whole
General practitioners’ perspectives on campaigns to promote rapid help-seeking behaviour at the onset of rheumatoid arthritis
Objective. To explore general practitioners’ (GPs’ ) perspectives on public health campaigns to encourage people with the early symptoms of rheumatoid arthritis (RA) to seek medical help rapidly. Design. Nineteen GPs participated in four semistructured focus groups. Focus groups were audio-recorded, transcribed verbatim, and analysed using thematic analysis. Results. GPs recognised the need for the early treatment of RA and identified that facilitating appropriate access to care was important. However, not all held the view that a delay in help seeking was a clinically significant issue. Furthermore, many were concerned that the early symptoms of RA were often non-specific, and that current knowledge about the nature of symptoms at disease onset was inadequate to inform the content of a help-seeking campaign. They argued that a campaign might not be able to specifically target those who need to present urgently. Poorly designed campaigns were suggested to have a negative impact on GPs’ workloads, and would “clog up” the referral pathway for genuine cases of RA. Conclusions. GPs were supportive of strategies to improve access to Rheumatological care and increase public awareness of RA symptoms. However, they have identified important issues that need to be considered in developing a public health campaign that forms part of an overall strategy to reduce time to treatment for patients with new onset RA. This study highlights the value of gaining GPs’ perspectives before launching health promotion campaigns
SN 2002cx: The Most Peculiar Known Type Ia Supernova
We present photometric and spectroscopic observations of supernova (SN)
2002cx, which reveal it to be unique among all observed type Ia supernovae (SNe
Ia). SN 2002cx exhibits a SN 1991T-like premaximum spectrum, a SN 1991bg-like
luminosity, and expansion velocities roughly half those of normal SNe Ia.
Photometrically, SN 2002cx has a broad peak in the band and a plateau phase
in the band, and slow late-time decline. The color evolution is
nearly normal, but the and colors are very red. Early-time
spectra of SN 2002cx evolve very quickly and are dominated by lines from
Fe-group elements; features from intermediate-mass elements (Ca, S, Si) are
weak or absent. Mysterious emission lines are observed around 7000 \AA\ at
about 3 weeks after maximum brightness. The nebular spectrum of SN 2002cx is
also unique, consisting of narrow iron and cobalt lines. The observations of SN
2002cx are inconsistent with the observed spectral/photometric sequence, and
provide a major challenge to our understanding of SNe Ia. No existing
theoretical model can successfully explain all observed aspects of SN 2002cx.Comment: 60 pages, 12 figures. A high resolution PostScript version is
available at http://astro.berkeley.edu/~weidong/sn2002cx.p
Measuring with the ROSAT Deep Cluster Survey
We analyze the ROSAT Deep Cluster Survey (RDCS) to derive cosmological
constraints from the evolution of the cluster X-ray luminosity distribution.
The sample contains 103 galaxy clusters out to z=0.85 and flux-limit Flim=3
10^{-14} cgs (RDCS-3) in the [0.5-2.0] keV energy band, with a high-z extension
containing four clusters at 0.901 10^{-14} cgs (RDCS-1). Model
predictions for the cluster mass function are converted into the X-ray
luminosity function in two steps. First we convert mass into intra-cluster gas
temperature by assuming hydrostatic equilibrium. Then temperature is converted
into X-ray luminosity by using the most recent data on the Lx-T relation for
nearby and distant clusters. These include the Chandra data for seven distant
clusters at 0.57<z<1.27. From RDCS-3 we find \Omega_m=0.35+/-0.12 and
\sigma_8=0.66+/-0.06 for a spatially flat Universe with cosmological constant,
with no significant constraint on \Gamma . Even accounting for theoretical and
observational uncertainties in the mass/X-ray luminosity conversion, an
Einstein-de-Sitter model is always excluded at far more than the 3sigma level.Comment: 10 pages, 4 figures, to appear in Astrophysical Journa
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