Inhomogeneous Branching Processes: A Tale of Two Networks

A basic theme in probability is the use of simple approximations to study complex systems. In this thesis we leverage the humble branching process to tackle two problems on random graphs. First, we study a variant of linear preferential attachment graphs which includes a change point in the parameter set driving the attachment dynamics. Using a continuous-time branching process embedding, we show how to estimate the change point and prove its consistency via a functional central limit theorem for the number of leaves. Additionally, we analyze the long-range dependence in the evolution of the graph, showing in particular that the exponent of the degree distribution does not feel the effect of any change. Second, motivated by recent studies showing that the spread of viral content on the internet takes surprising shapes, we introduce a simple discrete-time model for social media cascades whereby the transmission probability of the cascade decays with the distance from source. We argue that such a cascade can be reasonably approximated by a generation-dependent Galton-Watson process with infinite mean, and, as a first step to understanding its growth behavior, derive a simple criteria for its extinction.Doctor of Philosoph

Porting or Not Porting? Availability of Exclusive Games in the Mobile App Market

Mobile games dominate the mobile app markets and contribute over half of the mobile app revenues. In order to attract more users and generate higher revenues, the platforms such as Apple iOS and Google Android, would like to partner with the game developers and have the developers exclusively stay at their own platforms to entice more consumer demands. For example, the game developer “Electronic Arts” agrees to offer Apple iOS a two-month exclusive window for the well-known mobile game “Plants vs. Zombies 2”. The benefits of the exclusivity to the platforms and app developers are unclear and not studies in the literature. This study aims (1) to provide managerial insights for the platforms and app developers, and (2) to analyze the pros and cons of the partnership strategy, e.g. when offering an exclusive deal, how do the platforms and developers maximize the corresponding profits by the exclusive deal, and what is the optimal exclusive duration

Melting in Superheated Silicon Films Under Pulsed-Laser Irradiation

This thesis examines melting in superheated silicon films in contact with SiO₂ under pulsed laser irradiation. An excimer-laser pulse was employed to induce heating of the film by irradiating the film through the transparent fused-quartz substrate such that most of the beam energy was deposited near the bottom Si-SiO₂ interface. Melting dynamics were probed via in situ transient reflectance measurements. The temperature profile was estimated computationally by incorporating temperature- and phase-dependent physical parameters and the time-dependent intensity profile of the incident excimer-laser beam obtained from the experiments. The results indicate that a significant degree of superheating occurred in the subsurface region of the film. Surface-initiated melting was observed in spite of the internal heating scheme, which resulted in the film being substantially hotter at and near the bottom Si-SiO₂ interface. By considering that the surface melts at the equilibrium melting point, the solid-phase-only heat-flow analysis estimates that the bottom Si-SiO₂ interface can be superheated by at least 220K during excimer-laser irradiation. It was found that at higher laser fluences (i.e., at higher temperatures), melting can be triggered internally. At heating rates of 10¹⁰ K/s, melting was observed to initiate at or near the (100)-oriented Si-SiO₂ interface at temperatures estimated to be over 300K above the equilibrium melting point. Based on theoretical considerations, it was deduced that melting in the superheated solid initiated via a nucleation and growth process. Nucleation rates were estimated from the experimental data using Johnson-Mehl-Avrami-Kolmogorov (JMAK) analysis. Interpretation of the results using classical nucleation theory suggests that nucleation of the liquid phase occurred via the heterogeneous mechanism along the Si-SiO₂ interface

Basic Psychological Needs Satisfaction of Online Learners’ Autonomous Self-Regulation in Higher Education

Online learners are oftentimes seen as a vague and abstract “variable” with barely no human face in the context of discussing how to optimize online learning. To see and hear online learners in the joint effort of meeting their complex needs which are essential to making them striving and fully functioning, we need to look into the autonomous self-regulation of online learners. In this session, we will share how basic psychological needs satisfaction predicts the autonomous self-regulation in the learner-centered teaching and learning of higher education

Observation of Superheating of Si at the Si/SiO2 Interface in Pulsed-laser irradiated Si Thin Films

Substantial superheating of single-crystal Si films at and near the bottom Si/SiO2 interface was observed. This was accomplished via back-side irradiation of a (100) single-crystal Si film on a quartz substrate using an excimer-laser pulse. The spatiotemporal details of the melting transition were tracked in situ using surface-side and substrate-side transient reflectance measurements, and the one-dimensional thermal profile evolution within the solid film during the heating period was numerically computed using the experimentally extracted temporal profile of the incident beam and temperature-dependent optical and thermal parameters of the materials. A simple lower-bound estimation identifies that superheating in excess of 100 K was attained within Si along the bottom (100)-Si/SiO2 interface even at moderate beam energy densities

The use of three-dimensional printing technology in orthopaedic surgery: A review

Three-dimensional (3-D) printing or additive manufacturing, an advanced technology that 3-D physical models are created, has been wildly applied in medical industries, including cardiothoracic surgery, cranio-maxillo-facial surgery and orthopaedic surgery. The physical models made by 3-D printing technology give surgeons a realistic impression of complex structures, allowing surgical planning and simulation before operations. In orthopaedic surgery, this technique is mainly applied in surgical planning especially revision and reconstructive surgeries, making patient-specific instruments or implants, and bone tissue engineering. This article reviews this technology and its application in orthopaedic surgery.published_or_final_versio

Predict Market Share with Users’ Online Activities Data: An Initial Study on Market Share and Search Index of Mobile Phone

Acquiring accurate and timely market share information is very important for producers to arrange producing plan and design marketing strategy. However the high cost and long period of collecting survey data in survey-based method make it much difficult to easily get latest market shares data. Recently, the emerging online web systems provide users with new and convenient ways of searching, learning, experiencing and buying products. The users’ activities data captured by these web systems can reflect users’ buying intentions and behaviours very well, and contain very valuable information for predicting market shares. In this study, the correlation between Google search index and market shares of mobile phones is analyzed with time series analysis technology. The experiment result shows the statistically significant relationships exist between search index and market shares. This indicates the easily got search index data with low cost has the power of timely forecasting market shares. This study opens a door to apply users’ online activities data to accurately and timely predict market shares, which will bring many benefits to producers and customers