Non-trivial flat connections on the 3-torus II: The exceptional groups F_4 and E_6,7,8

We continue the construction of non-trivial vacua for gauge theories on the 3-torus, started in hep-th/9901154. Application of constructions based on twist in SU(N) with N > 2 produce more extra vacua in theories with exceptional groups. We calculate the relevant unbroken subgroups, and their contribution to the Witten index. We show that the extra vacua we find in the exceptional groups are sufficient to solve the Witten index problem for these groups.Comment: LaTeX, 25 pages, 1 figur

Short range radio research in Twente

The research and education by the Telecommunication Engineering Group at the University of Twente is dedicated to physical layer topics in communications. Three research tracks have prominence: Short Range Radio, Microwave Photonics, and Electromagnetic Compatibility. Arjan is active in the Short Range Radio division, and will briefly outline the interests and activities of this group. Furthermore he will present some results of the research that he did during his short sabbatical in Belfast last year. This concerns the performance analysis of a frequency offset modulation scheme using wideband noise carriers. The main advantage of such a scheme is that it enables fast receiver synchronization without channel adaptation, while providing robustness to multipath fading and in-band interference. This is important for low-power wireless systems with bursty traffic, such as sensor networks. In the talk a semi-analytical framework for evaluating its bit error rate performance in wideband frequency-selective fading channels will be described. Some numerical results will be presented, based on channel models developed in the IEEE 802.15.4a channel modeling subgroup. These illustrate that the considered system can be designed with a lower fading margin than a narrowband system

Gift-Exchange, Incentives, and Heterogeneous Workers

By incorporating reciprocity in an otherwise standard principal-agent model, I investigate the relation between monetary gift-exchange and incentive pay, while allowing for worker heterogeneity. I assume that some, but not all, workers care more for their principal when they are convinced that the principal cares for them. The principal can be egoistic or altruistic. Absent worker heterogeneity, an altruistic principal signals his altruism by offering relatively weak incentives and a relatively high expected total compensation. However, the latter is not always required to credibly signal altruism. Furthermore, since some workers do not reciprocate the principal’s altruism, the principal may find it optimal to write a contract that simultaneously signals his altruism and screens reciprocal worker types. Such a contract is characterised by excessively strong incentives and a relatively high expected total compensation.reciprocity, gift-exchange, signaling game, incentive contracts, screening

Welfare and Distribution Effects of Water Pricing Policies

In this paper, distribution and welfare effects of changes in block price systems are evaluated. A method is discussed to determine, for a Marshallian demand function, equivalent variation in case of a block price system. The method is applied to analyze welfare and distribution effects of changing water prices in the Metropolitan Region of São Paulo. Results show that there is a trade off between average welfare and income distribution. A pro-poor price system may result in lower average welfare than a flat price system, but in higher individual welfare for the poor. Moreover, there is a trade off between revenues for the water company and income distribution. Even though pro-poor price systems may not be as good for average welfare as flat price systems, their direct effects on poverty are important. Introducing pro-poor price systems, however, may have financial consequences for the water companies.Water Demand, Welfare Economics, Equivalent Variation

Market concentration in the banking sector: Evidence from Albania

The market structure can be described by concentration ratios based on the oligopoly theory or the structure - conduct - performance paradigm. Measures of concentration and also competition are essential for banks conduction in the banking industry. Several researchers have proved concentration level to be major determinants of banking system efficiency. Theoretical characteristics of market concentration measures are illustrated with empirical evidence. The market structure of the Albanian Banking Sector has changed dramatically in recent years. On 1990s, our country has experienced deregulation, foreign bank penetration, and an accelerated process of consolidation and competition in the banking sector. Particularly, the working paper examines the nature and the extent of changes in market concentration of Albanian banking sector. It focused primarily on a descriptive and dynamic analysis of change in the concentration indices in banking sector from year to year. Also it examines how the inherited structure of the banking system affects the way of the distribution of market shares amongst the different banks that comprise on the banking sector. --Bank Concentration,Concentration ratios,HHI index,Market Structure

On Non-Parallelizable Deterministic Client Puzzle Scheme with Batch Verification Modes

A (computational) client puzzle scheme enables a client to prove to a server that a certain amount of computing resources (CPU cycles and/or Memory look-ups) has been dedicated to solve a puzzle. Researchers have identified a number of potential applications, such as constructing timed cryptography, fighting junk emails, and protecting critical infrastructure from DoS attacks. In this paper, we first revisit this concept and formally define two properties, namely deterministic computation and parallel computation resistance. Our analysis show that both properties are crucial for the effectiveness of client puzzle schemes in most application scenarios. We prove that the RSW client puzzle scheme, which is based on the repeated squaring technique, achieves both properties. Secondly, we introduce two batch verification modes for the RSW client puzzle scheme in order to improve the verification efficiency of the server, and investigate three methods for handling errors in batch verifications. Lastly, we show that client puzzle schemes can be integrated with reputation systems to further improve the effectiveness in practice