Mean Field Methods for a Special Class of Belief Networks

The chief aim of this paper is to propose mean-field approximations for a broad class of Belief networks, of which sigmoid and noisy-or networks can be seen as special cases. The approximations are based on a powerful mean-field theory suggested by Plefka. We show that Saul, Jaakkola and Jordan' s approach is the first order approximation in Plefka's approach, via a variational derivation. The application of Plefka's theory to belief networks is not computationally tractable. To tackle this problem we propose new approximations based on Taylor series. Small scale experiments show that the proposed schemes are attractive

Energy demand models for policy formulation : a comparative study of energy demand models

This paper critically reviews existing energy demand forecasting methodologies highlighting the methodological diversities and developments over the past four decades in order to investigate whether the existing energy demand models are appropriate for capturing the specific features of developing countries. The study finds that two types of approaches, econometric and end-use accounting, are used in the existing energy demand models. Although energy demand models have greatly evolved since the early 1970s, key issues such as the poor-rich and urban-rural divides, traditional energy resources, and differentiation between commercial and non-commercial energy commodities are often poorly reflected in these models. While the end-use energy accounting models with detailed sector representations produce more realistic projections compared with the econometric models, they still suffer from huge data deficiencies especially in developing countries. Development and maintenance of more detailed energy databases, further development of models to better reflect developing country context, and institutionalizing the modeling capacity in developing countries are the key requirements for energy demand modeling to deliver richer and more reliable input to policy formulation in developing countries.Energy Production and Transportation,Energy Demand,Environment and Energy Efficiency,Energy and Environment,Economic Theory&Research

Brane Intersections in the Presence of a Worldvolume Electric Field

The study of brane intersections has provided important insights into a possible non-commutative structure of spacetime geometry. In this paper we focus on the D1$\bot$D3 system. We compare the D1 and D3 descriptions of the interesection and search for non-static solutions of the D3$\bot$D1 funnel equations in the presence of a worldvolume electric field. We find that the D1 and D3 descriptions do not agree. We find time dependent solutions that are a natural generalization of those found without the electric field.Comment: 10 page

CP Violation and Flavour Mixings in Orbifold GUTs

We address the flavour problem by incorporating the hypothesis of universal strength of Yukawa couplings in the framework of a 5D GUT model compactified on an $S^1/(Z_2 \times Z_2^{\prime})$ orbifold. We show that a quantitatively successful picture of fermion masses and mixings emerges from the interplay between the bulk suppression factors of geometric origin and the phases of the Yukawa matrices. We give an explicit example, where we obtain a good fit for both the CKM and PMNS matrices.Comment: 8 pages, no figures; v2: minor changes, published in Phys Rev D (Rapid Communication

Upper bounds on all R-parity-violating \lambda\lambda'' combinations from proton stability

In an R-parity-violating supersymmetric theory, we derive upper bounds on all the \lambda''_{ijk}\lambda_{i'j'k'}-type combinations from the consideration of proton stability, where \lambda''_{ijk} are baryon-number-violating couplings involving three baryonic fields and \lambda_{i'j'k'} are lepton-number-violating couplings involving three leptonic fields.Comment: 5 pages, Latex, uses axodraw.sty; minor changes in the text. Final versio

Mini-grid based electrification in Bangladesh: Technical configuration and business analysis

AbstractThis paper presents a local level study of a village off-grid system in Bangladesh. It applies an integrated methodology that identifies the demand in the off-grid village context using alternative scenarios. The techno-economic analysis of the optimal off-grid system architecture is then presented using HOMER software. Three energy resources are considered, namely solar energy, wind and diesel fuel. The optimal configuration suggested for the scenarios consists of diesel generators for the basic level of demand and PV-diesel hybrid for higher demand and reliable supply scenarios. The cost of electricity per kWh remains high for the basic level of supply and decreases as the system size increases. However, the capital and asset replacement costs increased considerably for bigger systems. The business case is then analysed for each scenario and it was found that it is practically impossible to reach grid price parity even with full capital cost subsidy, indicating significant amount of operating cost subsidy requirement that makes the larger systems financially unsustainable. Moreover, the small mini-grid system for the basic level of supply emerges as a cheaper option than providing the consumers with solar home systems. But the monthly electricity bill will become unaffordable for most consumers when demand restrictions are removed. Accordingly, the paper suggests a mini-grid based electricity supply to provide the basic level of provision alongside productive energy use during off-peak hours as the starting point. If the business develops and the demand improves, the system can be expanded subsequently using appropriate technology combinations