43,500 research outputs found
Generalised Compositional Theories and Diagrammatic Reasoning
This chapter provides an introduction to the use of diagrammatic language, or
perhaps more accurately, diagrammatic calculus, in quantum information and
quantum foundations. We illustrate the use of diagrammatic calculus in one
particular case, namely the study of complementarity and non-locality, two
fundamental concepts of quantum theory whose relationship we explore in later
part of this chapter.
The diagrammatic calculus that we are concerned with here is not merely an
illustrative tool, but it has both (i) a conceptual physical backbone, which
allows it to act as a foundation for diverse physical theories, and (ii) a
genuine mathematical underpinning, permitting one to relate it to standard
mathematical structures.Comment: To appear as a Springer book chapter chapter, edited by G.
Chirabella, R. Spekken
A new stellar mixing process operating below shell convection zones following off-center ignition
During most stages of stellar evolution the nuclear burning of lighter to
heavier elements results in a radial composition profile which is stabilizing
against buoyant acceleration, with light material residing above heavier
material. However, under some circumstances, such as off-center ignition, the
composition profile resulting from nuclear burning can be destabilizing, and
characterized by an outwardly increasing mean molecular weight. The potential
for instabilities under these circumstances, and the consequences that they may
have on stellar structural evolution, remain largely unexplored. In this paper
we study the development and evolution of instabilities associated with
unstable composition gradients in regions which are initially stable according
to linear Schwarzschild and Ledoux criteria. In particular, we explore the
mixing taking place under various conditions with multi-dimensional
hydrodynamic convection models based on stellar evolutionary calculations of
the core helium flash in a 1.25 \Msun star, the core carbon flash in a
9.3\,\Msun star, and of oxygen shell burning in a star with a mass of
23\,\Msun. The results of our simulations reveal a mixing process associated
with regions having outwardly increasing mean molecular weight that reside
below convection zones. The mixing is not due to overshooting from the
convection zone, nor is it due directly to thermohaline mixing which operates
on a timescale several orders of magnitude larger than the simulated flows.
Instead, the mixing appears to be due to the presence of a wave field induced
in the stable layers residing beneath the convection zone which enhances the
mixing rate by many orders of magnitude and allows a thermohaline type mixing
process to operate on a dynamical, rather than thermal, timescale. We discuss
our results in terms of related laboratory phenomena and associated theoretical
developments.Comment: accepted for publication in Astrophysical Journal, 9 pages, 8 figure
Concentration fluctuations and phase transitions in coupled modulated bilayers
We consider the formation of finite-size domains in lipid bilayers consisting
of saturated and hybrid lipids. First, we describe a monolayer model that
includes a coupling between a compositional scalar field and a two-dimensional
vectorial order-parameter. Such a coupling yields an effective two-dimensional
microemulsion free-energy for the lipid monolayer, and its characteristic
length of compositional modulations can be considered as the origin of
finite-size domains in biological membranes. Next, we consider a coupled
bilayer composed of two modulated monolayers, and discuss the static and
dynamic properties of concentration fluctuations above the transition
temperature. We also investigate the micro-phase separation below the
transition temperature, and compare the micro-phase separated structures with
statics and dynamics of concentration fluctuations above the transition.Comment: 14 pages, 12 figures, 1 tabl
Design of crystal-like aperiodic solids with selective disorder--phonon coupling
Functional materials design normally focuses on structurally-ordered systems
because disorder is considered detrimental to many important physical
properties. Here we challenge this paradigm by showing that particular types of
strongly-correlated disorder can give rise to useful characteristics that are
inaccessible to ordered states. A judicious combination of low-symmetry
building unit and high-symmetry topological template leads to aperiodic
"procrystalline" solids that harbour this type of topological disorder. We
identify key classes of procrystalline states together with their
characteristic diffraction behaviour, and establish a variety of mappings onto
known and target materials. Crucially, the strongly-correlated disorder we
consider is associated with specific sets of modulation periodicities
distributed throughout the Brillouin zone. Lattice dynamical calculations
reveal selective disorder-phonon coupling to lattice vibrations characterised
by these same periodicities. The principal effect on the phonon spectrum is to
bring about dispersion in energy rather than wave-vector, as in the
poorly-understood "waterfall" effect observed in relaxor ferroelectrics. This
property of procrystalline solids suggests a mechanism by which
strongly-correlated topological disorder might allow new and useful
functionalities, including independently-optimised thermal and electronic
transport behaviour as required for high-performance thermoelectrics.Comment: 4 figure
Process algebra for performance evaluation
This paper surveys the theoretical developments in the field of stochastic process algebras, process algebras where action occurrences may be subject to a delay that is determined by a random variable. A huge class of resource-sharing systems – like large-scale computers, client–server architectures, networks – can accurately be described using such stochastic specification formalisms. The main emphasis of this paper is the treatment of operational semantics, notions of equivalence, and (sound and complete) axiomatisations of these equivalences for different types of Markovian process algebras, where delays are governed by exponential distributions. Starting from a simple actionless algebra for describing time-homogeneous continuous-time Markov chains, we consider the integration of actions and random delays both as a single entity (like in known Markovian process algebras like TIPP, PEPA and EMPA) and as separate entities (like in the timed process algebras timed CSP and TCCS). In total we consider four related calculi and investigate their relationship to existing Markovian process algebras. We also briefly indicate how one can profit from the separation of time and actions when incorporating more general, non-Markovian distributions
Statistical mechanics characterization of spatio-compositional inhomogeneity
On the basis of a model system of pillars built of unit cubes, a
two-component entropic measure for the multiscale analysis of
spatio-compositional inhomogeneity is proposed. It quantifies the statistical
dissimilarity per cell of the actual configurational macrostate and the
theoretical reference one that maximizes entropy. Two kinds of disorder
compete: i) the spatial one connected with possible positions of pillars inside
a cell (the first component of the measure), ii) the compositional one linked
to compositions of each local sum of their integer heights into a number of
pillars occupying the cell (the second component). As both the number of
pillars and sum of their heights are conserved, the upper limit for a pillar
height hmax occurs. If due to a further constraint there is the more demanding
limit h <= h* < hmax, the exact number of restricted compositions can be then
obtained only through the generating function. However, at least for systems
with exclusively composition degrees of freedom, we show that the neglecting of
the h* is not destructive yet for a nice correlation of the h*-constrained
entropic measure and its less demanding counterpart, which is much easier to
compute. Given examples illustrate a broad applicability of the measure and its
ability to quantify some of the subtleties of a fractional Brownian motion,
time evolution of a quasipattern [28,29] and reconstruction of a laser-speckle
pattern [2], which are hardly to discern or even missed.Comment: 17 pages, 5 figure
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