Diffuse optical spectroscopy (DOS) techniques characterize scattering media by examining their optical response to laser illumination. Time-domain DOS methods involve illuminating the medium with a laser pulse and using a fast photodetector to measure the time-dependent intensity of light that exits the medium after multiple scattering events. While DOS research traditionally focused on characterizing biological tissues, we demonstrate that time-domain diffuse optical measurements can also be used to characterize snow. We introduce a model that predicts the time-dependent reflectance of a dry snowpack as a function of its density, grain size, and black carbon content. We develop an algorithm that retrieves these properties from measurements at two wavelengths. To validate our approach, we assembled a two-wavelength lidar system to measure the time-dependent reflectance of snow samples with varying properties. Rather than measuring direct surface returns, our system captures photons that enter and exit the snow at different points, separated by a small distance (4–10 cm). We observe clear, linear correlations between our retrievals of density and black carbon concentration, and ground truth. For black carbon concentration the correlation is nearly one-to-one. We also find that our method is capable of distinguishing between small and large grain sizes.

The Vela pulsar (J0835$-$4510) is known to exhibit variations in Faraday rotation and dispersion on multi-decade timescales due to the changing sightline through the surrounding Vela supernova remnant and the Gum Nebula. Until now, variations in Faraday rotation towards Vela have not been studied on timescales less than around a decade. We present the results of a high-cadence observing campaign carried out with the Aperture Array Verification System 2 (AAVS2), a prototype SKA-Low station, which received a significant bandwidth upgrade in 2022. We collected observations of the Vela pulsar and PSR J0630$-$2834 (a nearby pulsar located outside the Gum Nebula), spanning $\sim$1 and $\sim$0.3 yr, respectively, and searched for linear trends in the rotation measure (RM) as a function of time. We do not detect any significant trends on this timescale ($\sim$months) for either pulsar, but the constraints could be greatly improved with more accurate ionospheric models. For the Vela pulsar, the combination of our data and historical data from the published literature have enabled us to model long-term correlated trends in RM and dispersion measure (DM) over the past two decades. We detect a change in DM of $\sim$0.3 $\mathrm{cm}^{-3}\,\mathrm{pc}$ which corresponds to a change in electron density of $\sim$$10^5\,\mathrm{cm}^{-3}$ on a transverse length scale of $\sim$1–2 au. The apparent magnetic field strength in the time-varying region changes from $240^{+30}_{-20}\,\mu\mathrm{G}$ to $-6.2^{+0.7}_{-0.9}\,\mu\mathrm{G}$ over the time span of the dataset. As well as providing an important validation of polarimetry, this work highlights the pulsar monitoring capabilities of SKA-Low stations, and the niche science opportunities they offer for high-precision polarimetry and probing the microstructure of the magneto-ionic interstellar medium.

We investigate the diversity in the sizes and average surface densities of the neutral atomic hydrogen (H i) gas discs in $\sim$280 nearby galaxies detected by the Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY). We combine the uniformly observed, interferometric H i data from pilot observations of the Hydra cluster and NGC 4636 group fields with photometry measured from ultraviolet, optical, and near-infrared imaging surveys to investigate the interplay between stellar structure, star formation, and H i structural parameters. We quantify the H i structure by the size of the H i relative to the optical disc and the average H i surface density measured using effective and isodensity radii. For galaxies resolved by $>$$1.3$ beams, we find that galaxies with higher stellar masses and stellar surface densities tend to have less extended H i discs and lower H i surface densities: the isodensity H i structural parameters show a weak negative dependence on stellar mass and stellar mass surface density. These trends strengthen when we limit our sample to galaxies resolved by $>$2 beams. We find that galaxies with higher H i surface densities and more extended H i discs tend to be more star forming: the isodensity H i structural parameters have stronger correlations with star formation. Normalising the H i disc size by the optical effective radius (instead of the isophotal radius) produces positive correlations with stellar masses and stellar surface densities and removes the correlations with star formation. This is due to the effective and isodensity H i radii increasing with mass at similar rates while, in the optical, the effective radius increases slower than the isophotal radius. Our results are in qualitative agreement with previous studies and demonstrate that with WALLABY we can begin to bridge the gap between small galaxy samples with high spatial resolution H i data and large, statistical studies using spatially unresolved, single-dish data.

Given the importance of angiostrongyliasis as an emerging infectious disease of humans, companion animals, and wildlife, the current study focused on the transmission dynamics of first- and third-stage larvae of the parasitic nematode, Angiostrongylus cantonensis. The migration of infective larvae and their subsequent distribution within the Lymnaeidae snail, Bullastra lessoni, were investigated over time using microscopic examination of histological sections and fresh tissue. Snails were divided into four anatomical regions: (i) anterior and (ii) posterior cephalopedal masses, (iii) mantle skirt and (iv) visceral mass. The viability of free-swimming third-stage larvae, after their release from snail tissues, was evaluated in vitro by propidium iodide staining and infectivity by in vivo infection of Wistar rats. Snails were sequentially dissected over time to assess the number and anatomical distribution of larvae within each snail and hence infer their migration pathway. Herein, ongoing larval migratory activity was detected over 28 days post-infection. A comparison of infection rates and the larval distribution within the four designated snail regions demonstrated a significant relationship between anatomical region and density of infective larvae, with larvae mostly distributed in the anterior cephalopedal mass (43.6 ± 10.8%) and the mantle skirt (33.0 ± 8.8%). Propidium iodide staining showed that free-swimming third-stage larvae retained viability for between 4 and 8 weeks when stored under laboratory conditions. In contrast to viability, larval infectivity in rats remained for up to 2 weeks only. Knowledge gained from the current work could provide information on the development of new approaches to controlling the transmission of this parasite.