Relativistic Charged Balls

It is proven that the relativistic charged ball with its charge less than its mass (in natural units) cannot have a non-singular static configuration while its radius approaches its external horizon size. This conclusion does not depend on the details of charge distribution and the equation of state. The involved assumptions are (1) the ball is made of perfect fluid, (2) the energy density is everywhere non-negative.Comment: revtex, 11 page

Evolving Effective Micro Behaviors for Real-Time Strategy Games

Real-Time Strategy games have become a new frontier of artificial intelligence research. Advances in real-time strategy game AI, like with chess and checkers before, will significantly advance the state of the art in AI research. This thesis aims to investigate using heuristic search algorithms to generate effective micro behaviors in combat scenarios for real-time strategy games. Macro and micro management are two key aspects of real-time strategy games. While good macro helps a player collect more resources and build more units, good micro helps a player win skirmishes against equal numbers of opponent units or win even when outnumbered. In this research, we use influence maps and potential fields as a basis representation to evolve micro behaviors. We first compare genetic algorithms against two types of hill climbers for generating competitive unit micro management. Second, we investigated the use of case-injected genetic algorithms to quickly and reliably generate high quality micro behaviors. Then we compactly encoded micro behaviors including influence maps, potential fields, and reactive control into fourteen parameters and used genetic algorithms to search for a complete micro bot, ECSLBot. We compare the performance of our ECSLBot with two state of the art bots, UAlbertaBot and Nova, on several skirmish scenarios in a popular real-time strategy game StarCraft. The results show that the ECSLBot tuned by genetic algorithms outperforms UAlbertaBot and Nova in kiting efficiency, target selection, and fleeing. In addition, the same approach works to create competitive micro behaviors in another game SeaCraft. Using parallelized genetic algorithms to evolve parameters in SeaCraft we are able to speed up the evolutionary process from twenty one hours to nine minutes. We believe this work provides evidence that genetic algorithms and our representation may be a viable approach to creating effective micro behaviors for winning skirmishes in real-time strategy games

Accounting quality across different groups of firms under differential reporting framework: UK evidence

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Motivation: The IASB and the UK ASB have adopted different financial reporting rules for different classes of company. The IASB have IFRS and IFRS for SMEs. In the UK, currently companies follow IFRS (for public companies), UK GAAP (for medium-sized companies) or FRSSE (for small companies). Furthermore, some companies are exempt from audit. It is difficult to evaluate the efficacy of this approach to regulation since the ASB (and IASB) do not specify what consequences should follow. Do they expect public companies have higher accounting quality than medium and small companies? Or do they expect accounting quality to be the same across different groups of companies? Objective: The main objective of this study is to examine accounting quality in order to inform the future policy and discussion about the differential reporting framework. We examine the effects of accounting standards across public, medium and small companies. However, companies also face reporting discipline from market forces, and consequently we also examine the impact of debt-holders on reporting quality across and within medium and small companies. Methodology: We measure accounting quality from different aspects. For the assessment of differential accounting standards, we use: the level of accruals (ratio of cash flows to earnings), earnings smoothing, and target beating. For the assessment of any debt-holders effect, we use aspects that are suited to their needs, namely: earnings conservatism, and earnings persistence. Main Findings: Under the discipline of accounting standards, we find that the financial reporting behaviour of medium sized entities is significantly different from public and small companies. This suggests that accounting standards do not equalise accounting quality. The impacts of debt-holders on accounting quality are generally weak within medium and small companies. This implies that accounting standards are the main discipline for financial reporting for medium and small companies, which is consistent with the suggestions of Ball and Shivakumar (2005). However, we raise a few issues concerning the interpretation of the accounting quality measurements (earnings conservatism and earnings persistence) and provide theoretical and empirical support for the discussion. Recommendations: We suggest the accounting regulations for private companies may need to be further strengthened, especially for medium-sized companies