9,018 research outputs found
Frequency selective lens antenna
A variant of the hemispherical microwave lens antenna is reported where the ground plane region is modified through use of a frequency selective surface. This allows discrimination of frequencies by two closely spaced primary feeds. A scale model is reported operating at 12 and 30 GHz
The SDSS-GALEX viewpoint of the truncated red sequence in field environments at z~0
We combine GALEX near-UV photometry with a volume-limited sample of local
(0.005<z<0.037) SDSS DR4 galaxies to examine the composition and the
environmental dependencies of the optical and UV-optical colour-magnitude (C-M)
diagrams. We find that ~30% of red sequence galaxies in the optical C-M diagram
show signs of ongoing star-formation from their spectra having EW(Halpha)>2A.
This contamination is greatest at faint magnitudes (Mr>-19) and in field
regions where as many as three-quarters of red sequence galaxies are
star-forming, and as such has important consequences for following the build-up
of the red sequence. We find that the NUV-r colour instead allows a much more
robust separation of passively-evolving and star-forming galaxies, which allows
the build-up of the UV-selected red sequence with redshift and environment to
be directly interpreted in terms of the assembly of stellar mass in
passively-evolving galaxies. We find that in isolated field regions the number
density of UV-optical red sequence galaxies declines rapidly at magnitudes
fainter than Mr~-19 and appears completely truncated at Mr~-18. This confirms
the findings of Haines et al. (2007) that no passively-evolving dwarf galaxies
are found more than two virial radii from a massive halo, whether that be a
group, cluster or massive galaxy. These results support the downsizing paradigm
whereby the red sequence is assembled from the top down, being already largely
in place at the bright end by z~1, and the faint end filled in at later epochs
in clusters and groups through environment-related processes such as
ram-pressure stripping or galaxy harassment.Comment: 12 pages, 7 figures, MNRAS submitte
Case studies of clear air turbulence using the diagnostic Richardson Number Tendency formulation
The results of four case studies of clear air turbulence (CAT) using the diagnostic Richardson number tendency (DRT) formulation are highlighted. The performance of this technique in resolving regions of documented CAT encounters is encouraging. Its operational adaptability appears particularly attractive in that input data can be supplied by the currently operational rawinsonde system. Two CAT indices are calculated deterministically, sensing synoptic scale changes in static stability and vertical wind shear conductive for supporting mesoscale CAT layers. These two indices reveal volumes of the troposphere which act as source regions for patches of CAT. The first, the time to reach the critical Richardson number necessary for the initiation of turbulent conditions, was first used by Oard (1974). A second index is devised which is an adaptation of Roach's (1970) work relating synoptic scale and mesoscale energetical coupling and gives more information on the relative intensity of these source regions. The output from the DRT computer module highlights specific regions of the atmosphere which can be interpreted operationally in terms of a CAT encounter probability
Aerodynamic penalties of heavy rain on a landing aircraft
The aerodynamic penalties of very heavy rain on landing aircraft were investigated. Based on severity and frequency of occurrence, the rainfall rates of 100 mm/hr, 500 mm/hr, and 2000 mm/hr were designated, respectively, as heavy, severe, and incredible. The overall and local collection efficiencies of an aircraft encountering these rains were calculated. The analysis was based on raindrop trajectories in potential flow about an aircraft. All raindrops impinging on the aircraft are assumed to take on its speed. The momentum loss from the rain impact was later used in a landing simulation program. The local collection efficiency was used in estimating the aerodynamic roughness of an aircraft in heavy rain. The drag increase from this roughness was calculated. A number of landing simulations under a fixed stick assumption were done. Serious landing shortfalls were found for either momentum or drag penalties and especially large shortfalls for the combination of both. The latter shortfalls are comparable to those found for severe wind shear conditions
Shapley Supercluster Survey: Ram-Pressure Stripping vs. Tidal Interactions in the Shapley Supercluster
We present two new examples of galaxies undergoing transformation in the
Shapley supercluster core. These low-mass (stellar mass from 0.4E10 to 1E10
Msun) galaxies are members of the two clusters SC-1329-313 (z=0.045) and
SC-1327-312 (z=0.049). Integral-field spectroscopy complemented by imaging in
ugriK bands and in Halpha narrow-band are used to disentangle the effects of
tidal interaction (TI) and ram-pressure stripping (RPS). In both galaxies,
SOS-61086 and SOS-90630, we observe one-sided extraplanar ionized gas extending
respectively 30kpc and 41kpc in projection from their disks. The galaxies'
gaseous disks are truncated and the kinematics of the stellar and gas
components are decoupled, supporting the RPS scenario. The emission of the
ionized gas extends in the direction of a possible companion for both galaxies
suggesting a TI. The overall gas velocity field of SOS-61086 is reproduced by
ad hoc N-body/hydrodynamical simulations of RPS acting almost face-on and
starting about 250Myr ago, consistent with the age of the young stellar
populations. A link between the observed gas stripping and the cluster-cluster
interaction experienced by SC-1329-313 and A3562 is suggested. Simulations of
ram pressure acting almost edge-on are able to fully reproduce the gas velocity
field of SOS-90630, but cannot at the same time reproduce the extended tail of
outflowing gas. This suggests that an additional disturbance from a TI is
required. This study adds a piece of evidence that RPS may take place in
different environments with different impacts and witnesses the possible effect
of cluster-cluster merger on RPS.Comment: 27 pages, 28 figures, MNRAS accepte
Evaluating the Effects of Scan Strategy on AM Annealed Fe-3Si steel through Understanding of Solidification Conditions and Thermal Stresses
Soft magnetic steels have seen recent adoption in additive manufacturing (AM) due to the prospect of reducing eddy currents and hysteresis losses through leveraging of complex geometries and microstructural control. An annealing step will be a significant step for these alloys produced in AM to increase grain size and further reduce hysteresis losses. In this study, thin wall Fe-3Si samples were produced using laser powder bed fusion (L-PBF) using two different scan strategies, with a subset of samples annealed at 1200°C for 5 minutes. The effects of the two different scan strategies on microstructure in the as-built and annealed samples were analyzed through EBSD where it was found that the scan strategy does have an effected on annealed microstructure. Thermal simulations using OpenFoam were used to rationalize the differences in microstructure formation between the two scan strategies for the as-built scan strategies by looking at the thermal gradients and solidification velocity, while explanations on why there is a difference in resulting annealed microstructure was made by looking at the grain orientation, size and misorientation. Further, thermal-mechanical simulations were conducted using Abaqus to see if differences in the resulting elastic and plastic strains due to differences in thermal stresses related to the two difference scan strategies could be a mechanism causing differences in annealed microstructure to occur
A concept for a fuel efficient flight planning aid for general aviation
A core equation for estimation of fuel burn from path profile data was developed. This equation was used as a necessary ingredient in a dynamic program to define a fuel efficient flight path. The resultant algorithm is oriented toward use by general aviation. The pilot provides a description of the desired ground track, standard aircraft parameters, and weather at selected waypoints. The algorithm then derives the fuel efficient altitudes and velocities at the waypoints
LoCuSS: Exploring the selection of faint blue background galaxies for cluster weak-lensing
Cosmological constraints from galaxy clusters rely on accurate measurements
of the mass and internal structure of clusters. An important source of
systematic uncertainty in cluster mass and structure measurements is the secure
selection of background galaxies that are gravitationally lensed by clusters.
This issue has been shown to be particular severe for faint blue galaxies. We
therefore explore the selection of faint blue background galaxies, by reference
to photometric redshift catalogs derived from the COSMOS survey and our own
observations of massive galaxy clusters at z~0.2. We show that methods relying
on photometric redshifts of galaxies in/behind clusters based on observations
through five filters, and on deep 30-band COSMOS photometric redshifts are both
inadequate to identify safely faint blue background galaxies. This is due to
the small number of filters used by the former, and absence of massive galaxy
clusters at redshifts of interest in the latter. We therefore develop a
pragmatic method to combine both sets of photometric redshifts to select a
population of blue galaxies based purely on photometric analysis. This sample
yields stacked weak-lensing results consistent with our previously published
results based on red galaxies. We also show that the stacked clustercentric
number density profile of these faint blue galaxies is consistent with
expectations from consideration of the lens magnification signal of the
clusters. Indeed, the observed number density of blue background galaxies
changes by ~10-30 per cent across the radial range over which other surveys
assume it to be flat.Comment: submitted to MNRA
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