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Saturn has long been the only giant planet in our solar system without any known Trojan members. In this paper, with serendipitous archival observations and refined orbit determination, we report that 2019 UO$_{14}$ is a Trojan of the gas giant. However, the object is only a transient Trojan currently librating around the leading Lagrange point $L_4$ of the Sun-Saturn system in a period of $\sim\!0.7$ kyr. Our N-body numerical simulation shows that 2019 UO$_{14}$ was likely captured as a Centaur and became trapped around $L_4$ $\sim\!2$ kyr ago from a horseshoe coorbital. The current Trojan state will be maintained for another millennium or thereabouts before transitioning back to a horseshoe state. Additionally, we characterize the physical properties of 2019 UO$_{14}$. Assuming a linear phase slope of $0.06 \pm 0.01$ mag/deg, the mean $r$-band absolute magnitude of the object was determined to be $H_r = 13.11 \pm 0.07$, with its color measured to be consistent with those of Jupiter and Neptune Trojans and not statistically different from Centaurs. Although the short-lived Saturn Trojan exhibited no compelling evidence of activity in the observations, we favour the possibility that it could be an active Trojan. If confirmed, 2019 UO$_{14}$ would be marked as the first active Trojan in our solar system. We conservatively determine the optical depth of dust within our photometric aperture to be $\lesssim\!10^{-7}$, corresponding to a dust mass-loss rate to be $\lesssim\!1$ kg s$^{-1}$, provided that the physical properties of dust grains resemble Centaur 29P/Schwassmann-Wachmann 1.

In AI-based histopathology, domain shifts are common and well-studied. However, this research focuses on stain and scanner variations, which do not show the full picture -- shifts may be combinations of other shifts, or "invisible" shifts that are not obvious but still damage performance of machine learning models. Furthermore, it is important for models to generalize to these shifts without expensive or scarce annotations, especially in the histopathology space and if wanting to deploy models on a larger scale. Thus, there is a need for "reactive" domain generalization techniques: ones that adapt to domain shifts at test-time rather than requiring predictions of or examples of the shifts at training time. We conduct a literature review and introduce techniques that react to domain shifts rather than requiring a prediction of them in advance. We investigate test time training, a technique for domain generalization that adapts model parameters at test-time through optimization of a secondary self-supervised task.

We present the analysis of the absorption troughs of six outflows observed in quasar SDSS J1130+0411 ($z \approx 3.98$) with radial velocities ranging from $-2400$ to $-15,400$ km s$^{-1}$. These spectra were taken with the Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph over the rest frame wavelength range of $1135-1890$ \r{A}. In the main outflow system ($v \approx -3200$ km s$^{-1}$), we identify Fe II and several Fe II* absorption troughs as well as Si II and Si II* troughs, which we use to determine the electron number density $\log n_e = 2.6_{-0.7}^{+0.8}$ cm$^{-3}$. Using the column densities of these and other ions, we determine a photoionization solution with hydrogen column density $\log N_H = 21.44_{-0.33}^{+0.24}$ cm$^{-2}$ and ionization parameter $\log U_H = -1.75_{-0.45}^{+0.28}$. From these values we derive the distance $R = 16_{-11}^{+23}$ kpc, the average mass flow rate $\dot{M} = 4100_{-2400}^{+6600}$ $M_{\odot}$ yr$^{-1}$, and the kinetic luminosity $\log \dot{E}_k = 46.13_{-0.37}^{+0.41}$ erg s$^{-1}$. This $\dot{E}_k$ is $1.4_{-0.8}^{+2.2}$% of the quasar's Eddington luminosity, and therefore contributes significantly to AGN feedback., Comment: 8 pages, 5 figures, 3 tables, published in MNRAS

We analyze the VLT/UVES spectrum of the quasar SDSS J143907.5-010616.7, retrieved from the UVES Spectral Quasar Absorption Database. We identify two outflow systems in the spectrum: a mini broad absorption line (mini-BAL) system and a narrow absorption line (NAL) system. We measure the ionic column densities of the mini-BAL ($v=-1550$ km s$^{-1}$) outflow, which has excited state absorption troughs of Fe II. We determine that the electron number density $\log{n_e}=3.4^{+0.1}_{-0.1}$ based on the ratios between the excited and ground state abundances of Fe II, and find the kinetic luminosity of the outflow to be $\lesssim 0.1 \%$ of the quasar's Eddington luminosity, making it insufficient to contribute to AGN feedback., Comment: 6 pages, 4 figures, accepted for publication in MNRAS