474 research outputs found
Separating weak lensing and intrinsic alignments using radio observations
We discuss methods for performing weak lensing using radio observations to
recover information about the intrinsic structural properties of the source
galaxies. Radio surveys provide unique information that can benefit weak
lensing studies, such as HI emission, which may be used to construct galaxy
velocity maps, and polarized synchrotron radiation; both of which provide
information about the unlensed galaxy and can be used to reduce galaxy shape
noise and the contribution of intrinsic alignments. Using a proxy for the
intrinsic position angle of an observed galaxy, we develop techniques for
cleanly separating weak gravitational lensing signals from intrinsic alignment
contamination in forthcoming radio surveys. Random errors on the intrinsic
orientation estimates introduce biases into the shear and intrinsic alignment
estimates. However, we show that these biases can be corrected for if the error
distribution is accurately known. We demonstrate our methods using simulations,
where we reconstruct the shear and intrinsic alignment auto and cross-power
spectra in three overlapping redshift bins. We find that the intrinsic position
angle information can be used to successfully reconstruct both the lensing and
intrinsic alignment power spectra with negligible residual bias.Comment: 17 pages, 10 figures, submitted to MNRA
Master of Science
thesisSix metal boride compounds (AlB2, MgB2, Al0.5Mg0.5B2, AlB12, AlMgB14 and SiB6) with particle sizes between 10-20 m were synthesized for insensitive energetic fuel additives from stoichiometric physical mixtures of elemental powders by high temperature solid state reaction. B4C was also investigated as a lower cost source of boron in AlB2 synthesis and showed promise as a boron substitute. Thermal analysis confirmed that the formation of boride compounds from physical mixtures decreased sensitivity to low temperature oxidation over the aluminum standard. Both Al+2B and AlB2 were much less sensitive to moisture degradation than aluminum in high humidity (10-100% relative humidity) and high temperature (20-80°C) environments. AlB2 was determined to be safe to store for extended periods of time in cool, dry environments. Impact, friction and shock sensitivity testing indicated that AlB2 and MgB2 were less sensitive than aluminum. The activation energies for the oxidation of Al, B, Al+2B and AlB2 were determined through an isothermal, isoconversional method in N2-20%O2 and O2 at one atmosphere. An activation energy of 413 ± 20 kJ/mol was calculated for AlB2 in O2. The incorporation of magnesium and/or aluminum with boron increased its oxidation rate and overall conversion through the formation of metal-borate crystals (2Al2O3·B2O3 and 3MgO·B2O3) which removed liquid B2O3 from the surface of oxidizing particles. Aluminum also increased the oxidation efficiency of B4C by a similar mechanism. AlB2, MgB2 and Al0.5Mg0.5B2 oxidized to greater than 85% of their theoretical values while exhibiting decreased sensitivity to low temperature oxidation, making them top candidates for further energetic testing. Cylinder expansion testing of AlMgB14 showed little reaction of the boride material within seven volume expansions, corresponding to poor energetic performance. Detonation calorimetry of AlB2 and Al + 2B using proprietary energetic mixtures in an argon atmosphere showed that AlB2 reacted almost completely while Al + 2B did not. Future work should focus on testing the diboride materials and synthesizing and testing similar materials made from B4C
Radio-Optical Galaxy Shape and Shear Correlations in the COSMOS Field using 3 GHz VLA Observations
We present a weak lensing analysis of the 3 GHz VLA radio survey of the
COSMOS field, which we correlate with overlapping HST-ACS optical observations
using both intrinsic galaxy shape and cosmic shear correlation statistics.
After cross-matching sources between the two catalogues, we measure the
correlations of galaxy position angles and find a Pearson correlation
coefficient of . This is a marked improvement from previous
studies which found very weak, or non-existent correlations, and gives insight
into the emission processes of radio and optical galaxies. We also extract
power spectra of averaged galaxy ellipticities (the primary observable for
cosmic shear) from the two catalogues, and produce optical-optical,
radio-optical and radio-radio spectra. The optical-optical auto-power spectrum
was measured to a detection significance of 9.80 and is consistent with
previous observations of the same field. For radio spectra (which we do not
calibrate, given the unknown nature of their systematics), although we do not
detect significant radio-optical (1.50) or radio-radio (1.45)
-mode power spectra, we do find the -mode spectra to be more consistent
with the shear signal expected from previous studies than with a null signal,
and vice versa for -mode and cross-correlation spectra. Our results
give promise that future radio weak lensing surveys with larger source number
densities over larger areas will have the capability to measure significant
weak lensing signals.Comment: 19 pages, 17 figures, accepted for publication in MNRA
Estimating the weak-lensing rotation signal in radio cosmic shear surveys
Weak lensing has become an increasingly important tool in cosmology and the
use of galaxy shapes to measure cosmic shear has become routine. The
weak-lensing distortion tensor contains two other effects in addition to the
two components of shear: the convergence and rotation. The rotation mode is not
measurable using the standard cosmic shear estimators based on galaxy shapes,
as there is no information on the original shapes of the images before they
were lensed. Due to this, no estimator has been proposed for the rotation mode
in cosmological weak-lensing surveys, and the rotation mode has never been
constrained. Here, we derive an estimator for this quantity, which is based on
the use of radio polarisation measurements of the intrinsic position angles of
galaxies. The rotation mode can be sourced by physics beyond CDM, and
also offers the chance to perform consistency checks of CDM and of
weak-lensing surveys themselves. We present simulations of this estimator and
show that, for the pedagogical example of cosmic string spectra, this estimator
could detect a signal that is consistent with the constraints from Planck. We
examine the connection between the rotation mode and the shear -modes and
thus how this estimator could help control systematics in future radio
weak-lensing surveys
Dynamic clay microstructures emerge via ion complexation waves
Clays control carbon, water and nutrient transport in the lithosphere,
promote cloud formation5 and lubricate fault slip through interactions among
hydrated mineral interfaces. Clay mineral properties are difficult to model
because their structures are disordered, curved and dynamic. Consequently,
interactions at the clay mineral-aqueous interface have been approximated using
electric double layer models based on single crystals of mica and atomistic
simulations. We discover that waves of complexation dipoles at dynamically
curving interfaces create an emergent long-range force that drives exfoliation
and restacking over time- and length-scales that are not captured in existing
models. Curvature delocalizes electrostatic interactions in ways that
fundamentally differ from planar surfaces, altering the ratio of ions bound to
the convex and concave sides of a layer. Multiple-scattering reconstruction of
low-dose energy-filtered cryo electron tomography enabled direct imaging of ion
complexes and electrolyte distributions at hydrated and curved mineral
interfaces with {\aa}ngstrom resolution over micron length scales. Layers
exfoliate and restack abruptly and repeatedly over timescales that depend
strongly on the counterion identity, demonstrating that the strong coupling
between elastic, electrostatic and hydration forces in clays promote collective
reorganization previously thought to be a feature only of active matter
Mathematical modelling of fibre-enhanced perfusion inside\ud a tissue-engineering bioreactor
We develop a simple mathematical model for forced flow of culture medium through a porous scaffold in a tissue- engineering bioreactor. Porous-walled hollow fibres penetrate the scaffold and act as additional sources of culture medium. The model, based on Darcy’s law, is used to examine the nutrient and shear-stress distributions throughout the scaffold. We consider several configurations of fibres and inlet and outlet pipes. Compared with a numerical solution of the full Navier–Stokes equations within the complex scaffold geometry, the modelling approach is cheap, and does not require knowledge of the detailed microstructure of the particular scaffold being used. The potential of this approach is demonstrated through quantification of the effect the additional flow from the fibres has on the nutrient and shear-stress distribution
Frontiers of Biogeography:Taking its place as a journal of choice for the publication of high quality biogeographical research articles
Through this editorial we seek your support and engagement as authors, readers and reviewers as we take the next steps in developing Frontiers of Biogeography as a leading international journal of biogeography and related subdisciplines. Here we make the case for submitting your next contribution to this journal: affordable, gold libre, open access, with the support of a disciplinarily-informed editorial and review team, which returns benefits to the biogeography community.Peer Reviewe
The role of algal organic matter in the separation of algae and cyanobacteria using the novel “Posi” - Dissolved air flotation process
Algae and cyanobacteria frequently require separation from liquid media in both water treatment and algae culturing for biotechnology applications. The effectiveness of cell separation using a novel dissolved air flotation process that incorporates positively charged bubbles (PosiDAF) has recently been of interest but has been shown to be dependent on the algae or cyanobacteria species tested. Previously, it was hypothesised that algal organic matter (AOM) could be impacting the separation efficiency. Hence, this study investigates the influence of AOM on cell separation using PosiDAF, in which bubbles are modified using a commercially available cationic polyelectrolyte poly(N, N-diallyl-N,N-dimethylammonium chloride) (PDADMAC). The separation of Chlorella vulgaris CS-42/7, Mychonastes homosphaera CS-556/01 and two strains of Microcystis aeruginosa (CS-564/01 and CS-555/1), all of which have similar cell morphology but different AOM character, was investigated. By testing the cell separation in the presence and absence of AOM, it was determined that AOM enhanced cell separation for all the strains but to different extents depending on the quantity and composition of carbohydrates and proteins in the AOM. By extracting AOM from the strain for which optimal separation was observed and adding it to the others, cell separation improved from 90%. This was attributed to elevated levels of acidic carbohydrates as well as glycoprotein-carbohydrate conjugations, which in turn were related to the nature and quantity of proteins and carbohydrates present in the AOM. Therefore, it was concluded that process optimisation requires an in-depth understanding of the AOM and its components. If culturing algae for biotechnology applications, this indicates that strain selection is not only important with respect to high value product content, but also for cell separation
Plutonium coordination and redox chemistry with the CyMe4-BTPhen polydentate N-donor extractant ligand
Complexation of Pu(IV) with the actinide extractant CyMe4-BTPhen (2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-1,10-phenanthroline) was followed by vis-NIR spectroscopy in acetonitrile solution. The solid-state structure of the crystallized product suggests that Pu(IV) is reduced to Pu(III) upon complexation. Analysis by DFT modeling is consistent with metal-based rather than ligand-based reduction
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