Relativistic Quantum Optics: On the relativistic invariance of the light-matter interaction models

In this note we discuss the invariance under general changes of reference frame of all the physical predictions of particle detector models in quantum field theory in general and, in particular, of those used in quantum optics to model atoms interacting with light. We find explicitly how the light-matter interaction Hamiltonians change under general coordinate transformations, and analyze the subtleties of the Hamiltonians commonly used to describe the light-matter interaction when relativistic motion is taken into account.Comment: 11 pages. ReVteX 4.1. V2: Updated to match published versio

Light and lightning at the end of the public tunnel : reform of the electricity sector in the Southern Cone

The authors provide an overview of recent privatization experiences in Argentina, Brazil, and Chile. They focus on both achievements and outstanding problems in the electricity sector. They pay special attention to the issue of whether regulators can enforce compliance and sustain the spirit of reform - bringing the forces of competition to the sector - despite the unavoidable adjustments and fine-tuning that effective regulation requires. Among the lessons: Competition, rather than privatization, is the key to transforming the sector. For competition to work, several conditions must be met: 1) The primary energy source must be competitive for competition in the wholesale market to work. (In Chile, the fact that most of the water rights have been allocated to the major generator company seriously limits efficiency in the sector.) 2) Monopolistic stages must be formally separate from other stages, with clear rules for third-party access. (Here, the structure adopted by Argentina seems superior to that adopted by Chile.) 3) New entry into the system is the ultimate test of competition. The main gain from competition in electricity generation comes from the decentralization of decisions about when, how much, and what type of generation has to be brought to the market, rather than from short-term gains from minimizing costs. Overall, vertical and horizontal separation in the sector increases rather than reduces the burden and complexity of regulation. In a disintegrated system, the issues that arose in a traditional monopoly situation (fair rate of return, asset base, tariff to final consumers, and so on) are significantly increased. New issues include third-party access, the promotion of competition, interconnection pricing, and consistency of regulations across stages of competitive development. Restructuring and privatization are still in their early stages so lessons drawn from experience must be considered tentative.Decentralization,Economic Theory&Research,Environmental Economics&Policies,Markets and Market Access,Labor Policies,Economic Theory&Research,Markets and Market Access,Access to Markets,Environmental Economics&Policies,Banks&Banking Reform

An introduction to financial and economic modeling for utility regulators

The most effective regulators in developing countriesare following remarkably similar approaches. The main common element across"best practice"countries is the use of relatively simple quantitative models of operators'behavior and constraints to measure the impact of regulatory decisions on some key financial and economic indicators of concern to the operators, the users, and the government. The authors provide an introduction to the design and use of these models. They draw on lessons from international experience in industrial and developing countries in ordinary or extraordinary revisions and in the context of contract renegotiations. Simplifying somewhat, these models force regulators to recognize that, in the long run, private operators need to at least cover their opportunity cost of capital, including the various types of risks specific to the country, the sector, or the projects with which they are involved. Because these variables change over time, scheduled revisions are needed to allow for adjustments in the key determinants of the rate of return of the operator. These revisions are a recognition of the fact that all these determinants-tariffs, subsidies, quality, investments, and other service obligations-are interrelated and jointly determine the rate of return. At every revision, the rules of the game for the regulator are exactly the same: to figure out the changes in the cost of capital and to adjust the variables driving the rate of return to ensure that it continues to be consistent with the cost of capital. If they can draw on reasonable data, these models do everything any financial model would do for the day-to-day management of a company but take a longer term view and include an explicit identification of the key regulatory instruments. They can monitor the consistency between cash flow generated by the business on the one hand and debt service and operational expense needs on the other to address the main concerns of the operators. They can also account for a large number of key policy factors including access and affordability concerns for various types of consumers. They generally account for the sensitivity of operators and users to various regulatory design options.Payment Systems&Infrastructure,Economic Theory&Research,Decentralization,Environmental Economics&Policies,Enterprise Development&Reform,Public Sector Economics&Finance,Environmental Economics&Policies,Economic Theory&Research,Banks&Banking Reform,Municipal Financial Management

Generic guide concepts for the European Spallation Source

The construction of the European Spallation Source (ESS) faces many challenges from the neutron beam transport point of view: The spallation source is specified as being driven by a 5 MW beam of protons, each with 2 GeV energy, and yet the requirements in instrument background suppression relative to measured signal vary between 10$^{-6}$ and 10$^{-8}$. The energetic particles, particularly above 20 MeV, which are expected to be produced in abundance in the target, have to be filtered in order to make the beamlines safe, operational and provide good quality measurements with low background. We present generic neutron guides of short and medium length instruments which are optimized for good performance at minimal cost. Direct line of sight to the source is avoided twice, with either the first point out of line of sight or both being inside the bunker (20\,m) to minimize shielding costs. These guide geometries are regarded as a baseline to define standards for instruments to be constructed at ESS. They are used to find commonalities and develop principles and solutions for common problems. Lastly, we report the impact of employing the over-illumination concept to mitigate losses from random misalignment passively, and that over-illumination should be used sparingly in key locations to be effective. For more widespread alignment issues, a more direct, active approach is likely to be needed

DSpot: Test Amplification for Automatic Assessment of Computational Diversity

Context: Computational diversity, i.e., the presence of a set of programs that all perform compatible services but that exhibit behavioral differences under certain conditions, is essential for fault tolerance and security. Objective: We aim at proposing an approach for automatically assessing the presence of computational diversity. In this work, computationally diverse variants are defined as (i) sharing the same API, (ii) behaving the same according to an input-output based specification (a test-suite) and (iii) exhibiting observable differences when they run outside the specified input space. Method: Our technique relies on test amplification. We propose source code transformations on test cases to explore the input domain and systematically sense the observation domain. We quantify computational diversity as the dissimilarity between observations on inputs that are outside the specified domain. Results: We run our experiments on 472 variants of 7 classes from open-source, large and thoroughly tested Java classes. Our test amplification multiplies by ten the number of input points in the test suite and is effective at detecting software diversity. Conclusion: The key insights of this study are: the systematic exploration of the observable output space of a class provides new insights about its degree of encapsulation; the behavioral diversity that we observe originates from areas of the code that are characterized by their flexibility (caching, checking, formatting, etc.).Comment: 12 page