5,862 research outputs found
Thermodynamic work from operational principles
In recent years we have witnessed a concentrated effort to make sense of
thermodynamics for small-scale systems. One of the main difficulties is to
capture a suitable notion of work that models realistically the purpose of
quantum machines, in an analogous way to the role played, for macroscopic
machines, by the energy stored in the idealisation of a lifted weight. Despite
of several attempts to resolve this issue by putting forward specific models,
these are far from capturing realistically the transitions that a quantum
machine is expected to perform. In this work, we adopt a novel strategy by
considering arbitrary kinds of systems that one can attach to a quantum thermal
machine and seeking for work quantifiers. These are functions that measure the
value of a transition and generalise the concept of work beyond the model of a
lifted weight. We do so by imposing simple operational axioms that any
reasonable work quantifier must fulfil and by deriving from them stringent
mathematical condition with a clear physical interpretation. Our approach
allows us to derive much of the structure of the theory of thermodynamics
without taking as a primitive the definition of work. We can derive, for any
work quantifier, a quantitative second law in the sense of bounding the work
that can be performed using some non-equilibrium resource by the work that is
needed to create it. We also discuss in detail the role of reversibility and
correlations in connection with the second law. Furthermore, we recover the
usual identification of work with energy in degrees of freedom with vanishing
entropy as a particular case of our formalism. Our mathematical results can be
formulated abstractly and are general enough to carry over to other resource
theories than quantum thermodynamics.Comment: 22 pages, 4 figures, axioms significantly simplified, more
comprehensive discussion of relationship to previous approache
Fourier Heat Conduction as a phenomenon described within the scope of the Second Law
The historical development of the Carnot cycle necessitated the construction
of isothermal and adiabatic pathways within the cycle that were also
mechanically "reversible" which lead eventually to the Kelvin-Clausius
development of the entropy function where the heat absorption is for the
diathermal (isothermal) paths of the cycle only. It is deduced from traditional
arguments that Fourier heat conduction involves mechanically "reversible" heat
transfer with irreversible entropy increase. Here we model heat conduction as a
thermodynamically reversible but mechanically irreversible process. The MD
simulations conducted shows excellent agreement with the theory. Such views and
results as these, if developed to a successful conclusion could imply that the
Carnot cycle be viewed as describing a local process of energy-work conversion
and that irreversible local processes might be brought within the scope of this
cycle, implying a unified treatment of thermodynamically (i) irreversible, (ii)
reversible, (iii) isothermal and (iv) adiabatic processes.Comment: 10 pages, 2 figures. Material for talk at conference and ICNPAA 2014
(Narvik, Norway) Conference Proceeding
Markovian Testing Equivalence and Exponentially Timed Internal Actions
In the theory of testing for Markovian processes developed so far,
exponentially timed internal actions are not admitted within processes. When
present, these actions cannot be abstracted away, because their execution takes
a nonzero amount of time and hence can be observed. On the other hand, they
must be carefully taken into account, in order not to equate processes that are
distinguishable from a timing viewpoint. In this paper, we recast the
definition of Markovian testing equivalence in the framework of a Markovian
process calculus including exponentially timed internal actions. Then, we show
that the resulting behavioral equivalence is a congruence, has a sound and
complete axiomatization, has a modal logic characterization, and can be decided
in polynomial time
Integrated Modeling and Verification of Real-Time Systems through Multiple Paradigms
Complex systems typically have many different parts and facets, with
different characteristics. In a multi-paradigm approach to modeling, formalisms
with different natures are used in combination to describe complementary parts
and aspects of the system. This can have a beneficial impact on the modeling
activity, as different paradigms an be better suited to describe different
aspects of the system. While each paradigm provides a different view on the
many facets of the system, it is of paramount importance that a coherent
comprehensive model emerges from the combination of the various partial
descriptions. In this paper we present a technique to model different aspects
of the same system with different formalisms, while keeping the various models
tightly integrated with one another. In addition, our approach leverages the
flexibility provided by a bounded satisfiability checker to encode the
verification problem of the integrated model in the propositional
satisfiability (SAT) problem; this allows users to carry out formal
verification activities both on the whole model and on parts thereof. The
effectiveness of the approach is illustrated through the example of a
monitoring system.Comment: 27 page
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