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Bars are important in the secular evolution of galaxies. This study is aimed at exploring the reasons why some galaxies have bars at redshift $z=0$ while others do not. We use ellipse fitting to measure the properties and evolution of bars in the IllustrisTNG cosmological simulation. By using the K-S two-sample test and tracing their evolutionary changes, we analyze the parameter differences between barred and unbarred galaxies. The properties of galaxies with short bars are also studied. When tracing all disk galaxies at $z=0$ back to $z=1$, all of them show similar bar features at $z=1$. The fraction of bars increases in barred and short-bar galaxies but decreases in unbarred galaxies during $z=1-0$. In the case of disk galaxies with stellar mass log$(M_*/M_\odot)> 10.8$, nurture (mainly mergers) plays the most important role in suppressing or destroying bars. Bars are more likely to endure in galaxies that experience fewer mergers, which can be quantified by smaller stellar halos and ex-situ mass fractions. Approximately 60\% of the unbarred galaxies in the local Universe once had a bar. In contrast, the lack of responsiveness to bar instabilities (a larger Toomre-Q parameter) due to a less compact nature plays an important role in generating unbarred disk galaxies with stellar mass log$(M_*/M_\odot)<10.8$. Moreover, short bars generally form at a similar time to normal bars, during which they either grow mildly or contract significantly. The fact that IllustrisTNG simulations may produce too many short-bar galaxies indicates that the dynamical properties of the central regions in IllustrisTNG galaxies are less likely to be affected by external factors, such as mergers and gas inflows., Comment: 17 pages, 14 figures, submitted to A&A

Most galaxies follow well-defined scaling relations of metallicity and stellar mass; however, some outliers at the low mass end of the observed galaxy population exhibit unusually high metallicity for their mass. Understanding how these objects get to be so metal-rich is vital for understanding the role of feedback in galaxy formation. Using the TNG50 simulation, we explore the origins of this phenomenon. We identify 227 metal-rich, Compact Stellar Systems (CSSs) that deviate significantly from this scaling relation. These CSSs are satellites located in the vicinity of massive host galaxies, with stellar masses ranging from $10^{8} M_{\odot}$ to $10^{10} M_{\odot}$ (including six systems that are close analogs of the M31-M32 system). Contrary to the previously assumed scenario that such objects are predominantly products of tidal stripping, our results suggest a more prevalent role for ram pressure in their formation. Indeed, 76\% (173) of these CSSs are formed through a burst of star formation occurring around the time of the first pericentric passage, typically at redshifts $z\lesssim1$, aided by strong ram pressure and tidal forces. The high ram pressure, resulting from the CSSs' rapid motion near the halo center, facilitates metal enrichment, producing high-metallicity CSSs by confining the metal-rich gas from bursty star formation, which leads to distinct stellar populations characterized by enhanced metallicity as well as high $\alpha$-abundance. Only the remaining 24\% (54) of metal-rich CSSs are generated through the tidal stripping of massive progenitors. Our results further indicate that M32 is more likely to have formed through intense star formation events rather than through gradual, tidal stripping, thereby providing crucial insights into the nature of low mass, compact galaxy formation., Comment: 28 pages, 13 figures. Submitted

Enterprise chatbots, powered by generative AI, are emerging as key applications to enhance employee productivity. Retrieval Augmented Generation (RAG), Large Language Models (LLMs), and orchestration frameworks like Langchain and Llamaindex are crucial for building these chatbots. However, creating effective enterprise chatbots is challenging and requires meticulous RAG pipeline engineering. This includes fine-tuning embeddings and LLMs, extracting documents from vector databases, rephrasing queries, reranking results, designing prompts, honoring document access controls, providing concise responses, including references, safeguarding personal information, and building orchestration agents. We present a framework for building RAG-based chatbots based on our experience with three NVIDIA chatbots: for IT/HR benefits, financial earnings, and general content. Our contributions are three-fold: introducing the FACTS framework (Freshness, Architectures, Cost, Testing, Security), presenting fifteen RAG pipeline control points, and providing empirical results on accuracy-latency tradeoffs between large and small LLMs. To the best of our knowledge, this is the first paper of its kind that provides a holistic view of the factors as well as solutions for building secure enterprise-grade chatbots.", Comment: 8 pages, 6 figures, 2 tables, Preprint submission to ACM CIKM 2024

From the IllustrisTNG-50 simulation, a sample of 836 central disk galaxies with tiny stellar halos is chosen to study the inherent evolution of galaxies driven by nature. These galaxies are classified as compact, normal, or extended by referencing their locations on the mass-size ($M_\star-R_{\rm 1/2}$) diagram. This research demonstrates the distinctive evolutionary pathways of galaxies with different sizes in IllustrisTNG simulations, primarily driven by nature. It is confirmed that disk galaxies inherit the angular momentum of their parent dark matter halos. More compact galaxies form earlier within halos possessing lower specific angular momentum through heightened star formation during the early phase at redshifts above 2. During the later phase, the size of extended galaxies experiences more pronounced growth by accreting gas with high angular momentum. Additionally, we reveal that many key characteristics of galaxies are linked to their mass and size: (1) compact galaxies tend to exhibit higher metal content, proportional to the potential well $\frac{M_\star}{R_{\rm 1/2}}$, (2) compact galaxies host more massive bulges and black holes, and higher central concentration. Furthermore, our analysis indicates that galaxies of all types continue to actively engage in star formation, with no evident signs of quenching attributed to their varying sizes and angular momenta., Comment: 11 pages, 11 figures. Accepted for publication in A&A

Utilizing a kinematic decomposition of simulated galaxies, we focus on galaxies with tiny kinematically inferred stellar halos, indicative of weak external influences. We investigate the intricate interplay between internal (natural) and external (nurture) processes in shaping the scaling relationships of specific angular momentum ($j_\star$), stellar mass ($M_\star$), and size of disk galaxies within the IllustrisTNG simulation. The correlation among mass, size, and angular momentum of galaxies is examined by comparing simulations with observations and the theoretical predictions of the exponential hypothesis. Galaxies with tiny stellar halos exhibit a large scatter in the $j_\star$-$M_\star$ relation, which suggests that it is inherently present in their initial conditions. The analysis reveals that the disks of these galaxies adhere to the exponential hypothesis, resulting in a tight fiducial $j_\star$-$M_\star$-scale length (size) relation that is qualitatively consistent with observations. The inherent scatter in $j_\star$ provides a robust explanation for the mass-size relation and its substantial variability. Notably, galaxies that are moderately influenced by external processes closely adhere to a scaling relation akin to that of galaxies with tiny stellar halos. This result underscores the dominant role of internal processes in shaping the overall $j_\star$-$M_\star$ and mass-size relation, with external effects playing a relatively minor role in disk galaxies. Furthermore, the correlation between galaxy size and the virial radius of the dark matter halo exists but fails to provide strong evidence of the connection between galaxies and their parent dark matter halos., Comment: 11 pages, 9 figures, accepted for publication in A&A

In the field of intracity freight transportation, changes in order volume are significantly influenced by temporal and spatial factors. When building subsidy and pricing strategies, predicting the causal effects of these strategies on order volume is crucial. In the process of calculating causal effects, confounding variables can have an impact. Traditional methods to control confounding variables handle data from a holistic perspective, which cannot ensure the precision of causal effects in specific temporal and spatial dimensions. However, temporal and spatial dimensions are extremely critical in the logistics field, and this limitation may directly affect the precision of subsidy and pricing strategies. To address these issues, this study proposes a technique based on flexible temporal-spatial grid partitioning. Furthermore, based on the flexible grid partitioning technique, we further propose a continuous entropy balancing method in the temporal-spatial domain, which named TS-EBCT (Temporal-Spatial Entropy Balancing for Causal Continue Treatments). The method proposed in this paper has been tested on two simulation datasets and two real datasets, all of which have achieved excellent performance. In fact, after applying the TS-EBCT method to the intracity freight transportation field, the prediction accuracy of the causal effect has been significantly improved. It brings good business benefits to the company's subsidy and pricing strategies., Comment: 10 pages

Supervised learning algorithms based on Convolutional Neural Networks have become the benchmark for medical image segmentation tasks, but their effectiveness heavily relies on a large amount of labeled data. However, annotating medical image datasets is a laborious and time-consuming process. Inspired by semi-supervised algorithms that use both labeled and unlabeled data for training, we propose the PLGDF framework, which builds upon the mean teacher network for segmenting medical images with less annotation. We propose a novel pseudo-label utilization scheme, which combines labeled and unlabeled data to augment the dataset effectively. Additionally, we enforce the consistency between different scales in the decoder module of the segmentation network and propose a loss function suitable for evaluating the consistency. Moreover, we incorporate a sharpening operation on the predicted results, further enhancing the accuracy of the segmentation. Extensive experiments on three publicly available datasets demonstrate that the PLGDF framework can largely improve performance by incorporating the unlabeled data. Meanwhile, our framework yields superior performance compared to six state-of-the-art semi-supervised learning methods. The codes of this study are available at https://github.com/ortonwang/PLGDF.

Gas flows in the presence of two independently-rotating nested bars remain not fully understood, which is likely to play an important role in fueling the central black hole. We use high-resolution hydrodynamical simulations with detailed models of subgrid physics to study this problem. Our results show that the inner bar in double-barred galaxies can help drive gas flow from the nuclear ring to the center. In contrast, gas inflow usually stalls at the nuclear ring in single-barred galaxies. The inner bar causes a quasi-periodic inflow with a frequency determined by the difference between the two bar pattern speeds. We find that the star formation rate is higher in the model with two bars than in that with one bar. The inner bar in our model gradually weakens and dissolves due to gas inflow over a few billion years. Star formation produces metal-rich/$\alpha$-poor stars which slows the weakening of the inner bar, but does not halt its eventual decay. We also present a qualitative comparison of the gas morphology and kinematics in our simulations with those of observed double-barred galaxies., Comment: 19 pages, 13 figures, ApJ accepted. Comments welcome

In recent years, deep learning has become a breakthrough technique in assisting medical image diagnosis. Supervised learning using convolutional neural networks (CNN) provides state-of-the-art performance and has served as a benchmark for various medical image segmentation and classification. However, supervised learning deeply relies on large-scale annotated data, which is expensive, time-consuming, and even impractical to acquire in medical imaging applications. Active Learning (AL) methods have been widely applied in natural image classification tasks to reduce annotation costs by selecting more valuable examples from the unlabeled data pool. However, their application in medical image segmentation tasks is limited, and there is currently no effective and universal AL-based method specifically designed for 3D medical image segmentation. To address this limitation, we propose an AL-based method that can be simultaneously applied to 2D medical image classification, segmentation, and 3D medical image segmentation tasks. We extensively validated our proposed active learning method on three publicly available and challenging medical image datasets, Kvasir Dataset, COVID-19 Infection Segmentation Dataset, and BraTS2019 Dataset. The experimental results demonstrate that our PCDAL can achieve significantly improved performance with fewer annotations in 2D classification and segmentation and 3D segmentation tasks. The codes of this study are available at https://github.com/ortonwang/PCDAL.

Combining new HI data from a synergetic survey of ASKAP WALLABY and FAST with the ALFALFA data, we study the effect of ram pressure and tidal interactions in the NGC 4636 group. We develop two parameters to quantify and disentangle these two effects on gas stripping in HI-bearing galaxies: the strength of external forces at the optical-disk edge, and the outside-in extents of HI-disk stripping. We find that gas stripping is widespread in this group, affecting 80% of HI-detected non-merging galaxies, and that 41% are experiencing both types of stripping. Among the galaxies experiencing both effects, the two types of strengths are independent, while two HI-stripping extents moderately anticorrelate with each other. Both strengths are correlated with HI-disk shrinkage. The tidal strength is related to a rather uniform reddening of low-mass galaxies ($M_*<10^9\,\text{M}_\odot$) when tidal stripping is the dominating effect. In contrast, ram pressure is not clearly linked to the color-changing patterns of galaxies in the group. Combining these two stripping extents, we estimate the total stripping extent, and put forward an empirical model that can describe the decrease of HI richness as galaxies fall toward the group center. The stripping timescale we derived decreases with distance to the center, from $\mathord{\sim}1\,\text{Gyr}$ beyond $R_{200}$ to $\mathord{\lesssim}10\,\text{Myr}$ near the center. Gas-depletion happens $\mathord{\sim}3\,\text{Gyr}$ since crossing $2R_{200}$ for HI-rich galaxies, but much quicker for HI-poor ones. Our results quantify in a physically motivated way the details and processes of environmental-effects-driven galaxy evolution, and might assist in analyzing hydrodynamic simulations in an observational way., Comment: 44 pages, 22 figures, 5 tables, accepted for publication in ApJ. Tables 4 and 5 are also available in machine-readable form. Values of $f_\text{tid}$ are updated without influencing major results and conclusions

In Paper I we showed that clumps in high-redshift galaxies, having a high star formation rate density (\Sigma_SFR), produce disks with two tracks in the [Fe/H]-[\alpha/Fe] chemical space, similar to that of the Milky Way's (MW's) thin + thick disks. Here we investigate the effect of clumps on the bulge's chemistry. The chemistry of the MW's bulge is comprised of a single track with two density peaks separated by a trough. We show that the bulge chemistry of an N-body + smoothed particle hydrodynamics clumpy simulation also has a single track. Star formation within the bulge is itself in the high-\Sigma_SFR clumpy mode, which ensures that the bulge's chemical track follows that of the thick disk at low [Fe/H] and then extends to high [Fe/H], where it peaks. The peak at low metallicity instead is comprised of a mixture of in-situ stars and stars accreted via clumps. As a result, the trough between the peaks occurs at the end of the thick disk track. We find that the high-metallicity peak dominates near the mid-plane and declines in relative importance with height, as in the MW. The bulge is already rapidly rotating by the end of the clump epoch, with higher rotation at low [\alpha/Fe]. Thus clumpy star formation is able to simultaneously explain the chemodynamic trends of the MW's bulge, thin + thick disks and the Splash., Comment: 25 pages, in press at ApJ

From the TNG50 cosmological simulation we build a sample of 191 well-resolved barred galaxies with a stellar mass $\logMstar > 10$ at $z=0$. We search for box/peanut bulges (BPs) in this sample, finding them in 55\% of cases. We compute $\fbp$, the BP probability for barred galaxies as a function of $\Mstar$, and find that this rises to a plateau, as found in observations of nearby galaxies. The transition mass where $\fbp$ reaches half the plateau value is $\logMstar = 10.14$, consistent with the observational value within measurement errors. We show that this transition in $\fbp$ can be attributed to the youth of the bars at low $\Mstar$, which is a consequence of downsizing of galaxies. Young bars, being generally shorter and weaker, have not yet had time to form BPs. At high mass, while we find a plateau, the value is at $\sim 60\%$ whereas observations saturate at $100\%$. We attribute this difference to excessive heating in TNG50, due to merger activity and to numerical resolution effects. BPs in TNG50 tend to occur in galaxies with more quiescent merger histories. As a result, the main driver of whether a bar hosts a BP in TNG50 is not the galaxy mass, but how long and strong the bar is. Separating the BP sample into those that have visibly buckled and those that have not, we find that fully half of BP galaxies show clear signs of buckling, despite the excessive heating and limited vertical resolution of TNG50., Comment: 20 pages, 24 figures, 5 tables. Submitted to MNRAS

Producing labels for unlabeled data is error-prone, making semi-supervised learning (SSL) troublesome. Often, little is known about when and why an algorithm fails to outperform a supervised baseline. Using benchmark datasets, we craft five common real-world SSL data scenarios: few-label, open-set, noisy-label, and class distribution imbalance/misalignment in the labeled and unlabeled sets. We propose a novel algorithm called Contrastive Credibility Propagation (CCP) for deep SSL via iterative transductive pseudo-label refinement. CCP unifies semi-supervised learning and noisy label learning for the goal of reliably outperforming a supervised baseline in any data scenario. Compared to prior methods which focus on a subset of scenarios, CCP uniquely outperforms the supervised baseline in all scenarios, supporting practitioners when the qualities of labeled or unlabeled data are unknown., Comment: Accepted to AAAI '24

Recent studies illustrate the correlation between the angular momenta of cosmic structures and their Lagrangian properties. However, only baryons are observable and it is unclear whether they reliably trace the cosmic angular momenta. We study the Lagrangian mass distribution, spin correlation, and predictability of dark matter, gas, and stellar components of galaxy-halo systems using IllustrisTNG, and show that the primordial segregations between components are typically small. Their protoshapes are also similar in terms of the statistics of moment of inertia tensors. Under the common gravitational potential they are expected to exert the same tidal torque and the strong spin correlations are not destroyed by the nonlinear evolution and complicated baryonic effects, as confirmed by the high-resolution hydrodynamic simulations. We further show that their late-time angular momenta traced by total gas, stars, or the central galaxies, can be reliably reconstructed by the initial perturbations. These results suggest that baryonic angular momenta can potentially be used in reconstructing the parameters and models related to the initial perturbations., Comment: 8 pages, 5 figures, 1 table. Matches the accepted version in ApJ

The IllustrisTNG simulations reproduce the observed scaling relation between stellar specific angular momentum (sAM) $j_{\rm s}$ and mass $M_{\rm s}$ of central galaxies. We show that the local $j_{\rm s}$-$M_{\rm s}$ relation ${\rm log}\ j_{\rm s} = 0.55 \ {\rm log}\ M_{\rm s} + 2.77$ develops at $z\lesssim 1$ in disk-dominated galaxies. We provide a simple model that describes well such a connection between halos and galaxies. The index 0.55 of the $j_{\rm s}$-$M_{\rm s}$ relation comes from the product of the indices of the $j_{\rm tot}\propto M_{\rm tot}^{0.81}$, $M_{\rm tot}\propto M_{\rm s}^{0.67}$, and $j_{\rm s}\propto j_{\rm tot}$ relations, where $j_{\rm tot}$ and $M_{\rm tot}$ are overall sAM and mass of a halo. A non-negligible deviation from the tidal torque theory, which predicts $j_{\rm tot}\propto M_{\rm tot}^{2/3}$, should be included. This model further suggests that the stellar-to-halo mass ratio of disk galaxies increases monotonically following a nearly power-law function that is consistent with the latest dynamical measurements. Biased collapse, in which galaxies form from the inner and lower sAM portion of their parent halos, has a minor effect at low redshifts. The retention factor of angular momentum reaches $\sim 1$ in disk galaxies with strong rotations, and it correlates inversely with the mass fraction of the spheroidal component, which partially explains the morphological dependence of the $j_{\rm s}$-$M_{\rm s}$ relation., Comment: 10 pages, 5 figures, accpeted for publication on ApJL