Search for: All records

The controlled production of microbial growth has the potential to reduce groundwater flow in seepage and dewatering systems. Stimulating the growth of indigenous bacteria could clog the pore space and result in a substantial permeability reduction. This study investigated the spatial distribution of permeability reduction under different nutrient stimulation treatments of indigenous bacteria across 16 cm columns of Ottawa 50-70 sand. Spatially uniform permeability reductions of up to an order of magnitude were achieved using both a high glucose (50 mg L-1) and a low glucose (10 mg L-1) nutrient formulation. The overall permeability began to drop by day 2 and generally reached a minimum permeability by day 14. There was no noticeable difference in the final permeability nor the rate of permeability reduction between high and low glucose formulations. Upscaling of experiments is highly recommended for future studies on the spatial uniformity of microbial growth and biologically induced permeability reductions. 

We study the origin of misalignments between the stellar and star-forming gas components of simulated galaxies in the eagle simulations. We focus on galaxies with stellar masses ≥109 M⊙ at 0 ≤ z ≤ 1. We compare the frequency of misalignments with observational results from the SAMI survey and find that overall, eagle can reproduce the incidence of misalignments in the field and clusters, as well as the dependence on stellar mass and optical colour within the uncertainties. We study the dependence on kinematic misalignments with internal galaxy properties and different processes related to galaxy mergers and sudden changes in stellar and star-forming gas mass. We find that galaxy mergers happen in similar frequency in mis- and aligned galaxies, with the main difference being misaligned galaxies showing a higher tidal field strength and fraction of ex situ stars. We find that despite the environment being relevant in setting the conditions to misalign the star-forming gas, the properties internal to galaxies play a crucial role in determining whether the gas quickly aligns with the stellar component or not. Hence, galaxies that are more triaxial and more dispersion dominated display more misalignments because they are inefficient at realigning the star-forming gas towards the stellar angular momentum vector.

 

The distribution of gas and metals in the circumgalactic medium (CGM) plays a critical role in how galaxies evolve. The MUSE-ALMA Haloes survey combines MUSE, ALMA, and HST observations to constrain the properties of the multiphase gas in the CGM and the galaxies associated with the gas probed in absorption. In this paper, we analyse the properties of galaxies associated with 32 strong ${\rm H\, {\small I}}$ Ly-α absorbers at redshift 0.2 ≲ z ≲ 1.4. We detect 79 galaxies within ±500 kms−1 of the absorbers in our 19 MUSE fields. These associated galaxies are found at physical distances from 5.7 kpc and reach star formation rates as low as 0.1 M⊙ yr−1. The significant number of associated galaxies allows us to map their physical distribution on the Δv and b plane. Building on previous studies, we examine the physical and nebular properties of these associated galaxies and find the following: (i) 27/32 absorbers have galaxy counterparts and more than 50 per cent of the absorbers have two or more associated galaxies, (ii) the ${\rm H\, {\small I}}$ column density of absorbers is anticorrelated with the impact parameter (scaled by virial radius) of the nearest galaxy as expected from simulations, (iii) the metallicity of associated galaxies is typically larger than the absorber metallicity, which decreases at larger impact parameters. It becomes clear that while strong ${\rm H\, {\small I}}$ absorbers are typically associated with more than a single galaxy, we can use them to statistically map the gas and metal distribution in the CGM.

 

Can Augmented Reality (AR) immersion and interactivity dispel misconceptions and increase public understanding of science? The interdisciplinary team including USC’s Institute for Creative Technologies, the Rossier School of Education and the La Brea Tar Pits Museum, developed two AR engagements, one miniature “tabletop” and one life-sized “field” experience to investigate the differences in AR across qualitatively distinct designs on interactivity and visual immersion. Participants were able to take part in a “virtual active dig site” and discover fossils preserved in the asphalt seep; they were also able to walk amongst Mammoths in a virtual simulation of Los Angeles from 25,000 years ago. Learning goals for the experiences included: how and what types of plants and animals are entrapped in the tar pits; the similarities/differences between the LA ecosystem in the ice age vs. present; and how we use the scientific method of testing ideas with evidence and revising hypotheses. Design considerations made to evaluate the efficacy of achieving learning objectives, and engagement included: interactivity (selection and manipulation); levels of immersion (smartphone vs head-mounted display), aesthetics (high-fidelity vs low-poly 3D-models). Take-aways from pilot and formal user-studies include the ability to achieve strong interest and consistent learning with lower-fidelity AR; strong reactions to large-scale, life-sized events even with lower fidelity models; mini-experiences, large scale, and even 2D posters (control) can be engaging with the right narrative and framing. Further results from the “Pit-91” tabletop study are being analyzed and data collection on the “Field Experience” is set to investigate a life-sized experience. 

The gas cycling in the circumgalactic regions of galaxies is known to be multi-phase. The MUSE–ALMA Haloes survey gathers a large multi-wavelength observational sample of absorption and emission data with the goal to significantly advance our understanding of the physical properties of such CGM gas. A key component of the MUSE–ALMA Haloes survey is the multi-facility observational campaign conducted with VLT/MUSE, ALMA, and HST. MUSE–ALMA Haloes targets comprise 19 VLT/MUSE IFS quasar fields, including 32 zabs <0.85 strong absorbers with measured N(H i) ≥1018 cm−2 from UV-spectroscopy. We additionally use a new complementary HST medium program to characterize the stellar content of the galaxies through a 40-orbit three-band UVIS and IR WFC3 imaging. Beyond the absorber-selected targets, we detect 3658 sources all fields combined, including 703 objects with spectroscopic redshifts. This galaxy-selected sample constitutes the main focus of the current paper. We have secured millimeter ALMA observations of some of the fields to probe the molecular gas properties of these objects. Here, we present the overall survey science goals, target selection, observational strategy, data processing and source identification of the full sample. Furthermore, we provide catalogues of magnitude measurements for all objects detected in VLT/MUSE, ALMA, and HST broad-band images and associated spectroscopic redshifts derived from VLT/MUSE observations. Together, this data set provides robust characterization of the neutral atomic gas, molecular gas and stars in the same objects resulting in the baryon census of condensed matter in complex galaxy structures.

 

Hydrogen isotope ratios of sedimentary leaf waxes (δ²H_Waxvalues) are increasingly used to reconstruct past hydroclimate. Here, we add δ²H_Waxvalues from 19 lakes and four swamps on 15 tropical Pacific islands to an updated global compilation of published data from surface sediments and soils. Globally, there is a strong positive linear correlation between δ²H values of mean annual precipitation (δ²H_Pvalues) and the leaf waxesn‐C₂₉‐alkane (R² = 0.74,n = 665) andn‐C₂₈‐acid (R² = 0.74,n = 242). Tropical Pacific δ²H_Waxvalues fall within the predicted range of values based on the global calibration, and the largest residuals from the global regression line are no greater than those observed elsewhere, despite large uncertainties in δ²H_Pvalues at some Pacific sites. However, tropical Pacific δ²H_Waxvalues in isolation are not correlated with estimated δ²H_Pvalues from isoscapes or from isotope‐enabled general circulation models. Palynological analyses from these same Pacific sediment samples suggest no systematic relationship between any particular type of pollen distribution and deviations from the global calibration line. Rather, the poor correlations observed in the tropical Pacific are likely a function of the small range of δ²H_Pvalues relative to the typical residuals around the global calibration line. Our results suggest that δ²H_Waxvalues are currently most suitable for use in detecting large changes in precipitation in the tropical Pacific and elsewhere, but that ample room for improving this threshold exits in both improved understanding of δ²H variability in plants, as well as in precipitation.