1,503 research outputs found
Energy conversion in isothermal nonlinear irreversible processes - struggling for higher efficiency
First we discuss some early work of Ulrike Feudel on structure formation in
nonlinear reactions including ions and the efficiency of the conversion of
chemical into electrical energy. Then we give some survey about energy
conversion from chemical to higher forms of energy like mechanical, electrical
and ecological energy. We consider examples of energy conversion in several
natural processes and in some devices like fuel cells. Further, as an example,
we study analytically the dynamics and efficiency of a simple "active circuit"
converting chemical into electrical energy and driving currents which is
roughly modeling fuel cells. Finally we investigate an analogous ecological
system of Lotka - Volterra type consisting of an "active species" consuming
some passive "chemical food". We show analytically for both these models that
the efficiency increases with the load, reaches values higher then 50 percent
in a narrow regime of optimal load and goes beyond some maximal load abrupt to
zero.Comment: 25 pages, 4 figure
Fundamental of cryogenics (for superconducting RF technology)
This review briefly illustrates a few fundamental concepts of cryogenic
engineering, the technological practice that allows reaching and maintaining
the low-temperature operating conditions of the superconducting devices needed
in particle accelerators. To limit the scope of the task, and not to duplicate
coverage of cryogenic engineering concepts particularly relevant to
superconducting magnets that can be found in previous CAS editions, the
overview presented in this course focuses on superconducting radio-frequency
cavities.Comment: 20 pages, contribution to the CAS - CERN Accelerator School: Course
on High Power Hadron Machines; 24 May - 2 Jun 2011, Bilbao, Spai
The Geometry of Interaction of Differential Interaction Nets
The Geometry of Interaction purpose is to give a semantic of proofs or
programs accounting for their dynamics. The initial presentation, translated as
an algebraic weighting of paths in proofnets, led to a better characterization
of the lambda-calculus optimal reduction. Recently Ehrhard and Regnier have
introduced an extension of the Multiplicative Exponential fragment of Linear
Logic (MELL) that is able to express non-deterministic behaviour of programs
and a proofnet-like calculus: Differential Interaction Nets. This paper
constructs a proper Geometry of Interaction (GoI) for this extension. We
consider it both as an algebraic theory and as a concrete reversible
computation. We draw links between this GoI and the one of MELL. As a
by-product we give for the first time an equational theory suitable for the GoI
of the Multiplicative Additive fragment of Linear Logic.Comment: 20 pagee, to be published in the proceedings of LICS0
A Structural Approach to Reversible Computation
Reversibility is a key issue in the interface between computation and
physics, and of growing importance as miniaturization progresses towards its
physical limits. Most foundational work on reversible computing to date has
focussed on simulations of low-level machine models. By contrast, we develop a
more structural approach. We show how high-level functional programs can be
mapped compositionally (i.e. in a syntax-directed fashion) into a simple kind
of automata which are immediately seen to be reversible. The size of the
automaton is linear in the size of the functional term. In mathematical terms,
we are building a concrete model of functional computation. This construction
stems directly from ideas arising in Geometry of Interaction and Linear
Logic---but can be understood without any knowledge of these topics. In fact,
it serves as an excellent introduction to them. At the same time, an
interesting logical delineation between reversible and irreversible forms of
computation emerges from our analysis.Comment: 30 pages, appeared in Theoretical Computer Scienc
The involutions-as-principal types/ application-as-unification analogy
In 2005, S. Abramsky introduced various universal models of computation based on Affine Combinatory Logic, consisting of partial involutions over a suitable formal language of moves, in order to discuss reversible computation in a game-theoretic setting. We investigate Abramsky\u2019s models from the point of view of the model theory of \u3bb-calculus, focusing on the purely linear and affine fragments of Abramsky\u2019s Combinatory Algebras. Our approach stems from realizing a structural analogy, which had not been hitherto pointed out in the literature, between the partial involution interpreting a combinator and the principal type of that term, with respect to a simple types discipline for \u3bb-calculus. This analogy allows for explaining as unification between principal types the somewhat awkward linear application of involutions arising from Geometry of Interaction (GoI). Our approach provides immediately an answer to the open problem, raised by Abramsky, of characterising those finitely describable partial involutions which are denotations of combinators, in the purely affine fragment. We prove also that the (purely) linear combinatory algebra of partial involutions is a (purely) linear \u3bb-algebra, albeit not a combinatory model, while the (purely) affine combinatory algebra is not. In order to check the complex equations involved in the definition of affine \u3bb-algebra, we implement in Erlang the compilation of \u3bb-terms as involutions, and their execution
The Geometry of Synchronization (Long Version)
We graft synchronization onto Girard's Geometry of Interaction in its most
concrete form, namely token machines. This is realized by introducing
proof-nets for SMLL, an extension of multiplicative linear logic with a
specific construct modeling synchronization points, and of a multi-token
abstract machine model for it. Interestingly, the correctness criterion ensures
the absence of deadlocks along reduction and in the underlying machine, this
way linking logical and operational properties.Comment: 26 page
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