DESCRIBING URGENT EVENT DIFFUSION ON TWITTER USING NETWORK STATISTICS

In this dissertation, I develop a novel framework to study the diffusion of urgent events through the popular social media platform—Twitter. Based on my literature review, this is the first comprehensive study on urgent event diffusion through Twitter. I observe similar diffusion patterns among different data sets and adopt the "cross prediction" mode to handle the early time prediction problem. I show that the statistics from the network of Twitter retweets can not only provide profound insights about event diffusion, but also can be used to effectively predict user influence and topic popularity. The above findings are consistent across various experiment settings. I also demonstrate that linear models consistently outperform state-of-art nonlinear ones in both user and hashtag prediction tasks, possibly implying the strong log-linear relationship between selected prediction features and the responses, which potentially could be a general phenomenon in the case of urgent event diffusion

Cross-loop propagation of a quasi-periodic extreme-ultraviolet wave train triggered by successive stretching of magnetic field structures during a solar eruption

Solar extreme-ultraviolet (EUV) waves generally refer to large-scale disturbances propagating outward from sites of solar eruptions in EUV imaging observations. Using the recent observations from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO), we report a quasi-periodic wave train propagating outward at an average speed of $\sim$308 km s$^{-1}$. At least five wavefronts can be clearly identified with the period being $\sim$120 s. These wavefronts originate from the coronal loop expansion, which propagates with an apparent speed of $\sim$95 km s$^{-1}$, about 3 times slower than the wave train. In the absence of a strong lateral expansion, these observational results might be explained by the theoretical model of Chen et al. (2002), which predicted that EUV waves may have two components: a faster component that is a fast-mode magnetoacoustic wave or shock wave and a slower apparent front formed as a result of successive stretching of closed magnetic field lines. In this scenario, the wave train and the successive loop expansion we observed likely correspond to the fast and slow components in the model, respectively.Comment: 9 pages, 4 figure

Observation of two splitting processes in a partial filament eruption on the sun: the role of breakout reconnection

Partial filament eruptions have often been observed, however, the physical mechanisms that lead to filament splitting are not yet fully understood. In this study, we present a unique event of a partial filament eruption that undergoes two distinct splitting processes. The first process involves vertical splitting and is accompanied by brightenings inside the filament, which may result from internal magentic reconnection within the filament. Following the first splitting process, the filament is separated into an upper part and a lower part. Subsequently, the upper part undergoes a second splitting, which is accompanied by a coronal blowout jet. An extrapolation of the coronal magnetic field reveals a hyperbolic flux tube structure above the filament, indicating the occurrence of breakout reconnection that reduces the constraning field above. Consequently, the filament is lifted up, but at a nonuniform speed. The high-speed part reaches the breakout current sheet to generate the blowout jet, while the low-speed part falls back to the solar surface, resulting in the second splitting. In addition, continuous brightenings are observed along the flare ribbons, suggesting the occurrence of slipping reconnection process. This study presents, for the first time, the unambiguous observation of a two-stage filament splitting process, advancing our understanding of the complex dynamics of solar eruptions.Comment: 12 pages, 8 figure

Flexible magnetic suction impermeable membrane of vertical curtain water interception technology for strong seepage loose layer of coal mines

With abundant mineral resources, many types of mining industry and many mines, mining development in China has led to the decline of groundwater level around the mines, waste of water resources, water quality pollution, surface collapse, land degradation, reduction of vegetation cover, and different degrees of impact on groundwater resources and ecological environment. In order to solve the problems of water waste and ecological damage caused by the lateral recharge of water from the strong seepage loose layer to the mine pit, we proposed a vertical curtain water interception technology with flexible magnetic suction membrane to protect the groundwater resources and ecological environment of coal mines. We firstly studied the performance of the suction membrane material, developed the magnetic absorption suction membrane connection process, and carried out indoor tests of different suction membrane connection processes, then we conducted a 1 369 m strong seepage loose layer water interception curtain field test application in the test mine. The research results show that the impermeable membrane has low permeability coefficient, dense structure, high flexibility, resistance to deformation and durability, and is a good material for water cut, pollution control and seepage control, which can meet the requirements of vertical curtain for the strong seepage loose layer of the mine. The self-developed magnetic suction joint material and connection process solved the problems of shallow laying depth, joint leakage and complicated operation of existing connection processes such as overlapping lap, joint lock and joint box, etc. The construction depth of suction membrane curtain connected by magnetic suction joint is not limited by the connection conditions, and the water interception effect of magnetic suction joint connection process is better than that of overlapping lap and joint lock (joint box) connection process. Through the test of making, laying, connecting and backfilling the curtain into a wall with 2 kinds of flexible magnetic absorbent impermeable membranes, the gap at the joint of the impermeable membrane was reduced from 5-20 cm to 0, and the two adjacent impermeable membranes were closely connected as an organic whole, which reduced the water passage of the interception curtain at the joint. Through the mine-field site test, it was found that the water catchment pits below the curtain which had been filled with strong seepage loose layer water leakage for a long time, had dried up, and the water level of strong seepage loose layer outside the curtain had increased by 5.55-9.12 m, and the water level inside the curtain had decreased by 3.21-5.84 m, so the protection of strong seepage loose layer water resources had achieved good results

Epidemiological and genetic characteristics of swine pseudorabies virus in mainland China between 2012 and 2017

The outbreak of pseudorabies (PR) in many Bartha-K61 vaccinated farms in China in late 2011 has seriously damaged the pig industry of one of the largest producers of pork products in the world. To understand the epidemiological characteristics of the pseudorabies virus (PRV) strains currently prevalent in China, a total of 16,256 samples collected from pig farms suspected of PRV infection in 27 Provinces of China between 2012 and 2017 were evaluated for detection of PRV. Since the extensive use of gE-deleted PRV vaccine in China, the PRV-gE was applied for determining wild-type virus infection by PCR. Of the 16,256 samples detected, approximately 1,345 samples were positive for the detection of PRV-gE, yielding an average positive rate of 8.27%. The positive rates of PRV detection from 2012 to 2017 were 11.92% (153/1284), 12.19% (225/1846), 6.70% (169/2523), 11.10% (269/2424), 5.57% (147/2640), and 6.90% (382/5539), respectively. To understand the genetic characteristics of the PRV strains currently circulating, 25 PRV strains isolated from those PRV-gE positive samples were selected for further investigation. Phylogenetic analysis based on gB, gC, and gE showed that PRV strains prevalent in China had a remarkably distinct evolutionary relationship with PRVs from other countries, which might explain the observation that Bartha-K61 vaccine was unable to provide full protection against emergent strains. Sequence alignments identified many amino acid changes within the gB, gC, and gE proteins of the PRVs circulating in China after the outbreak compared to those from other countries or those prevalent in China before the outbreak; those changes also might affect the protective efficacy of previously used vaccines in China, as well as being associated in part with the increased virulence of the current PRV epidemic strains in China

Precision Measurements of Deuterium Isotope Effects on the Chemical Shifts of Backbone Nuclei in Proteins: Correlations with Secondary Structure

Precision NMR measurements of deuterium isotope effects on the chemical shifts of backbone nuclei in proteins (¹⁵N, ¹³CO, ¹³C_α, and ¹HN) arising from ¹H-to-²H substitutions at aliphatic carbon sites. Isolation of molecular species with a defined protonation/deuteration pattern at carbon-α/β positions allows distinguishing and accurately quantifying different isotope effects within the protein backbone. The isotope shifts measured in the partially deuterated protein ubiquitin are interpreted in terms of backbone geometry via empirical relationships describing the dependence of isotope shifts on (φ; ψ) backbone dihedral angles. Because of their relatively large magnitude and clear dependence on the protein secondary structure, the two- and three-bond backbone amide ¹⁵N isotope shifts, ²ΔN­(C_α,iD) and ³ΔN­(C_α,i‑1D), can find utility for NMR structural refinement of small-to-medium size proteins

Carbon Relaxation in ¹³C^α–H^α and ¹³C^α–D^α Spin Pairs as a Probe of Backbone Dynamics in Proteins

NMR methodology for the measurements of α-carbon <i>R</i>₁ and <i>R</i>_1ρ spin relaxation rates in ¹³C^α–H^α and ¹³C^α–D^α spin pairs of U-[¹³C; ¹⁵N] partially deuterated proteins is developed. The <i>intra</i>-HN­[CA] NMR experiment isolates carbon nuclei belonging to either ¹³C^α–H^α or ¹³C^α–D^α spin systems in the same protein sample prior to the measurement of ¹³C^α relaxation rates. The differences between <i>R</i>₁ and <i>R</i>₂ rates in the two spin pairs (Δ<i>R</i>₁, Δ<i>R</i>₂) eliminate all contributions to ¹³C^α decay rates not associated with direct ¹³C^α–¹H^α(D^α) dipolar interactions including chemical exchange and serve as robust measures of C^α–H^α(D^α) bond vector motions in proteins. The methodology is applied to the relaxation study of α-carbon sites in the protein ubiquitin at two temperatures. The measures of order of individual C^α–H^α(D^α) bond vectors (<i>S</i>²) in ubiquitin derived from the fitting of differential rates (Δ<i>R</i>₁, Δ<i>R</i>₂) unambiguously report on protein dynamics, thereby eliminating potential contributions from modulations of C^α–H^α(D^α) bond lengths by their environment. They are comparable to the ones obtained from a molecular dynamics simulation at 27 °C