A PHYSICS-BASED APPROACH TO MODELING WILDLAND FIRE SPREAD THROUGH POROUS FUEL BEDS

Wildfires are becoming increasingly erratic nowadays at least in part because of climate change. CFD (computational fluid dynamics)-based models with the potential of simulating extreme behaviors are gaining increasing attention as a means to predict such behavior in order to aid firefighting efforts. This dissertation describes a wildfire model based on the current understanding of wildfire physics. The model includes physics of turbulence, inhomogeneous porous fuel beds, heat release, ignition, and firebrands. A discrete dynamical system for flow in porous media is derived and incorporated into the subgrid-scale model for synthetic-velocity large-eddy simulation (LES), and a general porosity-permeability model is derived and implemented to investigate transport properties of flow through porous fuel beds. Note that these two developed models can also be applied to other situations for flow through porous media. Simulations of both grassland and forest fire spread are performed via an implicit LES code parallelized with OpenMP; the parallel performance of the algorithms are presented and discussed. The current model and numerical scheme produce reasonably correct wildfire results compared with previous wildfire experiments and simulations, but using coarser grids, and presenting complicated subgrid-scale behaviors. It is concluded that this physics-based wildfire model can be a good learning tool to examine some of the more complex wildfire behaviors, and may be predictive in the near future

China's Natural Gas Imports and Prospects

The project provides an overview of China’s current natural gas imports and key factors impacting its future imports. As part of its strategy to pursue cleaner energy sources, the Chinese government has pledged to consume more natural gas, which has historically been underrepresented in the country’s energy mix. To achieve its natural gas consumption goal, China’s demand for imported natural gas is expected to reach 124 billion cubic meters in 2020, more than tripling its imports in 2012 of 38 billion cubic meters. Cheap and abundant gas in the U.S., as a result of the shale gas revolution, has generated enormous interest in China about the possibility of importing LNG from the U.S. However, uncertainties surrounding U.S. natural gas export policies reinforced China’s impression that importing gas from the U.S. may be a difficult and prolonged process. Several studies predict that the future influx of gas from the U.S. into the international market will lead to a decline in natural gas prices worldwide. As a result, even if China does not import LNG from the U.S., it is likely to benefit from the decrease in LNG prices in the global market. The mere possibility of importing gas from the U.S. has given China more leverage in its negotiations with Russia over the China-Russia gas pipeline. Given the recent progress the two countries have made in their negotiations, it is expected that Russia and China will finalize the gas pipeline agreement by the end of 2014. By 2020, the pipeline is expected to deliver 68 billion cubic meters of gas annually from Russia to China, meeting more than half of China’s total demand for imported gas. A secured supply of pipeline gas from Russia may depress China’s appetite for LNG imports from additional sources including the U.S. In addition, China’s domestic factors – including the gas tariff mechanism and regulations on import rights and infrastructure – will impact its future LNG imports. The current state-mandated gas tariff mechanism in China has led to losses of gas importing companies, since the mandated gas prices are not sufficient to cover the costs of imported gas. High barriers for any non-state capital to enter the gas-importing sector have further hindered efficient investments made along the LNG import value chain. Favorable regulatory reforms will incentivize Chinese companies, in particular non-state enterprises, to pursue cheaper natural gas supplies overseas, thereby increasing China’s competitiveness as a gas importer in the international market

Cross-Promotion in Social Media: Choosing the Right Allies

This paper investigates the strategic use of cross-promotion for content producers in social media. In particular, we study how a producer chooses other producers to cross-promote so as to maximize the expected benefits of them cross-promoting him/her in return. Theories on homophily effect and social influence suggest that cross-promoted producers are more likely to cross-promote the initiator in return when they are in the similar categories or share more common friends and when the initiator has higher status. However, the cross-promotion from producers of different categories and social groups (i.e., share fewer common friends) tend to benefit the initiator more. The benefits also increase as the status of the initiator increases. We collected a panel of data consisting of 27,356 producers’ profile and status information, content categories, and their cross-promotion activities over a period of two months from YouTube. To test our hypotheses, we first employ a cox proportional hazard model to estimate the probability of cross-promotion in return. Then, we use a difference-in-differences method with panel fixed effects to evaluate the effect of cross-promotion in return on the initiator. Our results strongly support our hypotheses and provide valuable insights for both content producers and social media platforms

A new Copula-CoVaR approach incorporating the PSO-SVM for identifying systemically important financial institutions

The effective identification of systemically important financial institutions (SIFIs) is key to preventing and resolving systemic financial risks; thus, it is of great research significance for emerging countries to supervise SIFIs and manage systemic financial risks. Since traditional research on identifying SIFIs does not consider emerging machine learning models, it is difficult to properly fit the characteristics of actual financial institutions’ asset distribution. This paper proposes a new method for measuring SIFIs, integrating the PSO-SVM model into the Copula-CoVaR model. This new PSO-SVM-Copula-CoVaR model is meant to evaluate China’s SIFIs based on the publicly traded price data of Chinese listed financial institutions. The empirical results show that, compared with the traditional parameter method (GARCH model) and the nonparametric method (kernel density estimation), the marginal distribution estimation method using the PSO-SVM method can better fit the distribution of an institution’s financial asset return sequence. That is, the model proposed in this paper helps regulatory authorities improve the list of SIFIs more reasonably and implement effective regulatory measures

Participation of Different Forces and Coeducation in Peking University: From Reports of Newspaper Media, 1918-1920

It was an important achievement that Peking University abolished female forbiddance and implemented coeducation in Women’s Liberation Movement during the May 4th New Culture Movement. In this period, newspaper media kept up with the historical trend. As the leader of public opinion, Newspaper media intervened, reported and publicized the abolishment of female forbiddance and the implementation of coeducation in Peking University. It promoted the involvement of different social forces: the Principal of Peking University — Cai Yuanpei, female intellectuals, teachers and students of Peking university. These various forces played different roles in this trend. In their interaction, the abolishment of female forbiddance and the implementation of coeducation in Peking University began with appeals and debates and eventually ended with the realization. Furthermore, it aroused a nationwide impact in the education field. It not only reflects that coeducation in universities is a historical trend of democratization and modernization in higher education, but also indicates that newspaper media plays an indispensable role in Women’s Liberation Movement

Effect of oteracil in combination with gimeracil on longterm survival and postoperative complications in elderly patients undergoing radical surgery for biliary tract cancer

Purpose: To investigate the effect of oteracil (Oxo) in combination with gimeracil (CDHP) on long-term survival and postoperative complications in elderly patients undergoing radical surgery for biliary tract cancer (BTC).Methods: Clinical data for 70 patients who underwent radical surgery for BTC in the Oncology Department of the Changle People’s Hospital, Weifang, China from April 2017 to April 2018 were collected. The patients were equally assigned to group A and group B, based on odd or even hospitalization number. After surgery, patients in group A received the combination of Oxo and CDHP, while group B patients received gemcitabine only. Long-term survival and incidence of adverse reactions were compared.Results: Compared with group B, group A had higher total treatment effectiveness (p < 0.05), lower clinical indices (p < 0.05), lower BPI score (p < 0.001) and higher 3-year overall survival (p < 0.05).Conclusion: Combined use of oteracil and gimeracil significantly prolongs the survival time and reduce cancer pain in BTC patients, with minimal toxic and side effects. However, further clinical trials are required prior to application in clinical practice.&nbsp

Architecture Information Communication in Two OSS Projects: the Why, Who, When, and What

Architecture information is vital for Open Source Software (OSS) development, and mailing list is one of the widely used channels for developers to share and communicate architecture information. This work investigates the nature of architecture information communication (i.e., why, who, when, and what) by OSS developers via developer mailing lists. We employed a multiple case study approach to extract and analyze the architecture information communication from the developer mailing lists of two OSS projects, ArgoUML and Hibernate, during their development life-cycle of over 18 years. Our main findings are: (a) architecture negotiation and interpretation are the two main reasons (i.e., why) of architecture communication; (b) the amount of architecture information communicated in developer mailing lists decreases after the first stable release (i.e., when); (c) architecture communications centered around a few core developers (i.e., who); (d) and the most frequently communicated architecture elements (i.e., what) are Architecture Rationale and Architecture Model. There are a few similarities of architecture communication between the two OSS projects. Such similarities point to how OSS developers naturally gravitate towards the four aspects of architecture communication in OSS development.Comment: Preprint accepted for publication in Journal of Systems and Software, 202