12,864 research outputs found
Spectroscopic Confusion: Its Impact on Current and Future Extragalactic HI Surveys
We present a comprehensive model to predict the rate of spectroscopic
confusion in HI surveys, and demonstrate good agreement with the observable
confusion in existing surveys. Generically the action of confusion on the HI
mass function was found to be a suppression of the number count of sources
below the `knee', and an enhancement above it. This results in a bias, whereby
the `knee' mass is increased and the faint end slope is steepened. For ALFALFA
and HIPASS we find that the maximum impact this bias can have on the Schechter
fit parameters is similar in magnitude to the published random errors. On the
other hand, the impact of confusion on the HI mass functions of upcoming medium
depth interferometric surveys, will be below the level of the random errors. In
addition, we find that previous estimates of the number of detections for
upcoming surveys with SKA-precursor telescopes may have been too optimistic, as
the framework implemented here results in number counts between 60% and 75% of
those previously predicted, while accurately reproducing the counts of existing
surveys. Finally, we argue that any future single dish, wide area surveys of HI
galaxies would be best suited to focus on deep observations of the local
Universe (z < 0.05), as confusion may prevent them from being competitive with
interferometric surveys at higher redshift, while their lower angular
resolution allows their completeness to be more easily calibrated for nearby
extended sources.Comment: Accepted to MNRAS, 14 pages, 9 figures, 2 table
When is Stacking Confusing?: The Impact of Confusion on Stacking in Deep HI Galaxy Surveys
We present an analytic model to predict the HI mass contributed by confused
sources to a stacked spectrum in a generic HI survey. Based on the ALFALFA
correlation function, this model is in agreement with the estimates of
confusion present in stacked Parkes telescope data, and was used to predict how
confusion will limit stacking in the deepest SKA-precursor HI surveys. Stacking
with LADUMA and DINGO UDEEP data will only be mildly impacted by confusion if
their target synthesised beam size of 10 arcsec can be achieved. Any beam size
significantly above this will result in stacks that contain a mass in confused
sources that is comparable to (or greater than) that which is detectable via
stacking, at all redshifts. CHILES' 5 arcsec resolution is more than adequate
to prevent confusion influencing stacking of its data, throughout its bandpass
range. FAST will be the most impeded by confusion, with HI surveys likely
becoming heavily confused much beyond z = 0.1. The largest uncertainties in our
model are the redshift evolution of the HI density of the Universe and the HI
correlation function. However, we argue that the two idealised cases we adopt
should bracket the true evolution, and the qualitative conclusions are
unchanged regardless of the model choice. The profile shape of the signal due
to confusion (in the absence of any detection) was also modelled, revealing
that it can take the form of a double Gaussian with a narrow and wide
component.Comment: 11 pages, 6 figures, accepted to MNRA
Space Station alpha joint bearing
Perhaps the most critical structural system aboard the Space Station is the Solar Alpha Rotary Joint which helps align the power generation system with the sun. The joint must provide structural support and controlled rotation to the outboard transverse booms as well as power and data transfer across the joint. The Solar Alpha Rotary Joint is composed of two transition sections and an integral, large diameter bearing. Alpha joint bearing design presents a particularly interesting problem because of its large size and need for high reliability, stiffness, and on orbit maintability. The discrete roller bearing developed is a novel refinement to cam follower technology. It offers thermal compensation and ease of on-orbit maintenance that are not found in conventional rolling element bearings. How the bearing design evolved is summarized. Driving requirements are reviewed, alternative concepts assessed, and the selected design is described
Inducing Private Wildfire Risk Mitigation: Experimental Investigation of Measures on Adjacent Public Lands
Increasing private wildfire risk mitigation is an important part of the larger forest restoration policy challenge. Data from an economic experiment are used to evaluate the effectiveness of providing fuel treatments on public land adjacent to private land to induce private wildfire risk mitigation. Results show evidence of âcrowding outâ where public spending can decrease the level of private risk mitigation. However, a policy prescription that ameliorates this crowding out is identified. Participants undertake more mitigation when fuel treatments on publicly owned lands are conditional on a threshold level of private mitigation effort and information describing each participantâs spending is provided. Key Words:
Controlled radical polymerization of vinyl acetate mediated by a vanadium complex
Initiation of the polymerization of vinyl acetate with azobis(isobutyronitrile) in the presence of a vanadium bis(iminopyridine) complex generates vanadium-capped dormant polymer chains with excellent correlation between molecular weight and conversion and good molecular weight distributions.JID: 9610838; 2010/02/17 [aheadofprint]; 2010/03/09 [epublish]; ppublishSource type: Electronic(1
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