163,124 research outputs found
A Parser Generator Based on Earley\u27s Algorithm
Most parser generators are programs that take a context-free grammar specification for a language and generate a parser for that language. Usually, the parsers generated by these parser generators are based on some variations of LL(k) or LR(k) parsing algorithms. The parser generators discussed in this paper creates parsers based on Earlcy\u27s Algorithm. This parser generator creates parsers from any arbitrary context-free grammar specifications; even from ambiguous, cyclic, and unbounded look ahead grammar. These parsers are more powerful than LL(k) and LR(k) parsers and enable the user to create many new applications
Market Power and Windfall Profits in Emission Permit Markets
Although market power in permit markets has been examined in some detail following the seminal work of Hahn (1984), the effect of free allocation on price manipulation with market power in both output and permit market has not specifically been addressed. I show that in this case, the threshold for free allocation above which dominant firms will increase the permit price is below their emissions. In addition to being of general economic interest, this issue is relevant in the context of the EUETS. I find that European power generators received free allowances in excess of the derived threshold.Market power, emissions permit markets, air pollution, EU ETS, CO2, electricity generation, permit allocation, windfall profits, cost pass-through
A language-theoretic view on network protocols
Input validation is the first line of defense against malformed or malicious inputs. It is therefore critical that the validator (which is often part of the parser) is free of bugs. To build dependable input validators, we propose using parser generators for context-free languages. In the context of network protocols, various works have pointed at context-free languages as falling short to specify precisely or concisely common idioms found in protocols. We review those assessments and perform a rigorous, language-theoretic analysis of several common protocol idioms. We then demonstrate the practical value of our findings by developing a modular, robust, and efficient input validator for HTTP relying on context-free grammars and regular expressions
Hidden Role of Maxwell Superalgebras in the Free Differential Algebras of D=4 and D=11 Supergravity
The purpose of this paper is to show that the so-called Maxwell superalgebra
in four dimensions, which naturally involves the presence of a nilpotent
fermionic generator, can be interpreted as a hidden superalgebra underlying N =
1, D=4 supergravity extended to include a 2-form gauge potential associated to
a 2-index antisymmetric tensor. In this scenario, the theory is appropriately
discussed in the context of Free Differential Algebras (an extension of the
Maurer-Cartan equations to involve higher-degree differential forms). The study
is then extended to the Free Differential Algebra describing D=11 supergravity,
showing that, also in this case, there exists a super-Maxwell algebra
underlying the theory.
The same extra spinors dual to the nilpotent fermionic generators whose
presence is crucial for writing a supersymmetric extension of the Maxwell
algebras, both in the D=4 and in the D=11 case, turn out to be fundamental
ingredients also to reproduce the D=4 and D=11 Free Differential Algebras on
ordinary superspace, whose basis is given by the supervielbein. The analysis of
the gauge structure of the supersymmetric Free Differential Algebras is carried
on taking into account the gauge transformations from the hidden
supergroup-manifold associated with the Maxwell superalgebras.Comment: 23 pages, misprints corrected, some comments added, version published
in The European Physical Journal C. Contains some text overlap with the
author's PhD thesis arXiv:1802.0660
Open-closed strings: Two-dimensional extended TQFTs and Frobenius algebras
We study a special sort of 2-dimensional extended Topological Quantum Field
Theories (TQFTs) which we call open-closed TQFTs. These are defined on
open-closed cobordisms by which we mean smooth compact oriented 2-manifolds
with corners that have a particular global structure in order to model the
smooth topology of open and closed string worldsheets. We show that the
category of open-closed TQFTs is equivalent to the category of knowledgeable
Frobenius algebras. A knowledgeable Frobenius algebra (A,C,i,i^*) consists of a
symmetric Frobenius algebra A, a commutative Frobenius algebra C, and an
algebra homomorphism i:C->A with dual i^*:A->C, subject to some conditions.
This result is achieved by providing a generators and relations description of
the category of open-closed cobordisms. In order to prove the sufficiency of
our relations, we provide a normal form for such cobordisms which is
characterized by topological invariants. Starting from an arbitrary such
cobordism, we construct a sequence of moves (generalized handle slides and
handle cancellations) which transforms the given cobordism into the normal
form. Using the generators and relations description of the category of
open-closed cobordisms, we show that it is equivalent to the symmetric monoidal
category freely generated by a knowledgeable Frobenius algebra. Our formalism
is then generalized to the context of open-closed cobordisms with labeled free
boundary components, i.e. to open-closed string worldsheets with D-brane labels
at their free boundaries.Comment: 47 pages; LaTeX2e with xypic and pstricks macros; corrected typo
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