PiCANet: Learning Pixel-wise Contextual Attention for Saliency Detection

Contexts play an important role in the saliency detection task. However, given a context region, not all contextual information is helpful for the final task. In this paper, we propose a novel pixel-wise contextual attention network, i.e., the PiCANet, to learn to selectively attend to informative context locations for each pixel. Specifically, for each pixel, it can generate an attention map in which each attention weight corresponds to the contextual relevance at each context location. An attended contextual feature can then be constructed by selectively aggregating the contextual information. We formulate the proposed PiCANet in both global and local forms to attend to global and local contexts, respectively. Both models are fully differentiable and can be embedded into CNNs for joint training. We also incorporate the proposed models with the U-Net architecture to detect salient objects. Extensive experiments show that the proposed PiCANets can consistently improve saliency detection performance. The global and local PiCANets facilitate learning global contrast and homogeneousness, respectively. As a result, our saliency model can detect salient objects more accurately and uniformly, thus performing favorably against the state-of-the-art methods

Understanding the role of magnetic field evolution in the initiation and development of solar eruptions

This dissertation aims to understand the initiation and evolution of solar eruptions. The essential science questions to answer include: What is the role of magnetohydro dynamic (MHD) instabilities and magnetic reconnection in triggering and driving eruptions? What are the role of Kink Instability (KI) and Torus Instability (TI) in determining the successful and failed eruptions? What is the thermal behavior of flare precursors in the initiation stage of solar eruptions? Finally, how does the corona magnetic field respond to the flare eruptions? The dissertation mainly includes the following studies. First, this dissertation presents a multi-instrument study of the two precursor brightenings prior to the M6.5 flare with a focus on their thermal behavior in terms of time variations of temperature (T), electron number density (n), and emission measure (EM). This study quantitatively describes the differences in the thermal parameters at the precursor phase, measured by different instruments operating at different wavelength regimes and for different emission mechanisms. The precursor brightenings in the passbands of Hard X-rays (HXR), extreme ultraviolet (EUV), microwave (MW), and Ha are found to occur within a strong magnetic field region (1200 G) around the flaring polarity inversion line (PIL). Such a small energy release in the lower atmosphere may be related to the onset of the main flare. Second, a statistical analysis of torus instability (TI) and kink instability (KI) in solar eruptions is presented, in order to improve our understanding of the likelihood of a CME based on the observed TI parameter decay index and KI parameter twist number. It is found that TI plays an important role in distinguishing between ejective and confined flares, while KI is much less influential. However, TI is not a necessary condition for eruption. Some magnetic flux ropes (MFRs) in the TI-stable regime still manage to break through the strong strapping field and evolve into CMEs. It, therefore, implies that an additional driving mechanism, such as magnetic reconnection, may be involved in eruptions. Third, a study of the magnetic field evolution of the X5.4 flare with two magnetic field extrapolation methods: Non-linear-force-free field (NLFFF) and Non-force-free field (Non-FFF) extrapolations are included in this dissertation. It is found that this flare is most likely triggered by the tether-cutting reconnection and the subsequent DAI. Clear 3D back-reactions of increasing horizontal magnetic field (Bh) and decreasing inclination angle (F) of the magnetic field from the photosphere are presented in both NLFFF and Non-FFF. The back-reaction of the increasing downward Lorentz force (Fz) acting on the photosphere produced by the Non-FFF result spatially correlates with the flare initiating location in the DAI analysis. Last but not least, a study of analyzing the magnetic field structure of the sunspot light bridges in AR 12371 during the M6.5 flare is included in this dissertation. Analysis of the 3D NLFFF model shows a low-lying 3D magnetic canopy as well as a 3D current system. The most substantial difference between the LBs and umbrae is found in the overall magnetic topology in that the field lines emanating from the two LBs are more twisted than that from the neighboring umbrae. At the end, this dissertation briefly introduces the SolarDB, a cyberinfrastructure built for flare studies and photospheric vector magnetic field reconstruction taking advantage of machine learning (ML)/ deep learning (DL) tools, and future work about the MHD simulation for solar eruptions

Marriage Fraud

This Article examines the astonishing array of doctrines used to determine what constitutes marriage fraud. It begins by locating the traditional nineteenth-century annulment-by-fraud doctrine within the realm of contract fraud, observing that in the family law context fraudulent marriages were voidable solely at the option of the injured party. The Article then explains how, in the twentieth century, a massive expansion of public benefits tied to marriage prompted new marriage fraud doctrines to develop in various areas of the law, shifting the concept of the injured party from the defrauded spouse to the public at large. It proposes a framework for understanding these new doctrines by demonstrating that courts apply different tests for finding fraud depending on the value of the benefit sought compared to the cost to the individual of using marriage to obtain it. Furthermore, the Article argues that marriage is an ineffective means for distributing public benefits that serve specific objectives; in other words, marriage is being asked to do too much work. As a possible response to this problem, the Article concludes that lawmakers could disaggregate the components of marriage to which they attach public benefits. This would improve the efficacy of public benefits distribution without entirely dismantling the institution of marriage or jeopardizing the stability that it may provide to societ