272 research outputs found
Environments for sonic ecologies
This paper outlines a current lack of consideration for the environmental context of Evolutionary Algorithms used for the generation of music. We attempt to readdress this balance by outlining the benefits of developing strong coupling strategies between agent and en- vironment. It goes on to discuss the relationship between artistic process and the viewer and suggests a placement of the viewer and agent in a shared environmental context to facilitate understanding of the artistic process and a feeling of participation in the work. The paper then goes on to outline the installation ‘Excuse Me and how it attempts to achieve a level of Sonic Ecology through the use of a shared environmental context
From Quantum Mechanics to Quantum Field Theory: The Hopf route
We show that the combinatorial numbers known as {\em Bell numbers} are
generic in quantum physics. This is because they arise in the procedure known
as {\em Normal ordering} of bosons, a procedure which is involved in the
evaluation of quantum functions such as the canonical partition function of
quantum statistical physics, {\it inter alia}. In fact, we shall show that an
evaluation of the non-interacting partition function for a single boson system
is identical to integrating the {\em exponential generating function} of the
Bell numbers, which is a device for encapsulating a combinatorial sequence in a
single function. We then introduce a remarkable equality, the Dobinski
relation, and use it to indicate why renormalisation is necessary in even the
simplest of perturbation expansions for a partition function. Finally we
introduce a global algebraic description of this simple model, giving a Hopf
algebra, which provides a starting point for extensions to more complex
physical systems
Some useful combinatorial formulae for bosonic operators
We give a general expression for the normally ordered form of a function
F(w(a,a*)) where w is a function of boson annihilation and creation operators
satisfying [a,a*]=1. The expectation value of this expression in a coherent
state becomes an exact generating function of Feynman-type graphs associated
with the zero-dimensional Quantum Field Theory defined by F(w). This enables
one to enumerate explicitly the graphs of given order in the realm of
combinatorially defined sequences. We give several examples of the use of this
technique, including the applications to Kerr-type and superfluidity-type
hamiltonians.Comment: 8 pages, 3 figures, 17 reference
Heisenberg-Weyl algebra revisited: Combinatorics of words and paths
The Heisenberg-Weyl algebra, which underlies virtually all physical
representations of Quantum Theory, is considered from the combinatorial point
of view. We provide a concrete model of the algebra in terms of paths on a
lattice with some decomposition rules. We also discuss the rook problem on the
associated Ferrers board; this is related to the calculus in the normally
ordered basis. From this starting point we explore a combinatorial underpinning
of the Heisenberg-Weyl algebra, which offers novel perspectives, methods and
applications.Comment: 5 pages, 3 figure
A generic Hopf algebra for quantum statistical mechanics
In this paper, we present a Hopf algebra description of a bosonic quantum
model, using the elementary combinatorial elements of Bell and Stirling
numbers. Our objective in doing this is as follows. Recent studies have
revealed that perturbative quantum field theory (pQFT) displays an astonishing
interplay between analysis (Riemann zeta functions), topology (Knot theory),
combinatorial graph theory (Feynman diagrams) and algebra (Hopf structure).
Since pQFT is an inherently complicated study, so far not exactly solvable and
replete with divergences, the essential simplicity of the relationships between
these areas can be somewhat obscured. The intention here is to display some of
the above-mentioned structures in the context of a simple bosonic quantum
theory, i.e. a quantum theory of non-commuting operators that do not depend on
space-time. The combinatorial properties of these boson creation and
annihilation operators, which is our chosen example, may be described by
graphs, analogous to the Feynman diagrams of pQFT, which we show possess a Hopf
algebra structure. Our approach is based on the quantum canonical partition
function for a boson gas.Comment: 8 pages/(4 pages published version), 1 Figure. arXiv admin note: text
overlap with arXiv:1011.052
Role of thyroid hormones in early postnatal development of skeletal muscle and its implications for undernutrition
Published online by Cambridge University Press 09 Mar 2007Energy intake profoundly influences many endocrine axes which in turn play a central role in development. The specific influence of a short period of mild hypothyroidism, similar to that induced by undernutrition, in regulating muscle development has been assessed in a large mammal during early postnatal life. Hypothyroidism was induced by providing methimazole and iopanoic acid in the feed of piglets between 4 and 14 d of age, and controls were pair-fed to the energy intake of their hypothyroid littermates. Thyroid status was evaluated, and myofibre differentiation and cation pump concentrations were then assessed in the following functionally distinct muscles: longissimus dorsi (l. dorsi), soleus and rhomboideus. Reductions in plasma concentrations of thyroxine (T4; 32%, P < O·Ol), triiodothyronine (T3;48%, P < 0·001), free T3, (58%, P < 0·001)and hepatic 5'-monodeiodinase (EC 1.11.1.8) activity (74%, P < 0·001) occurred with treatment. Small, although significant, increases in the proportion of type I slow-twitch oxidative fibres occurred with mild hypothyroidism, in l. dorsi (2%, P < 0·01) and soleus(7%, P < 0·01). Nuclear T3-receptor concentration in l. dorsi of hypothyroid animals compared with controls increased by 46% (P < 0·001), a response that may represent a homeostatic mechanism making muscle more sensitive to low levels of circulating thyroid hormones. Nevertheless, Na+, K+-ATPase (EC 3.6.1.37) concentration was reduced by 15–16% in all muscles (l.dorsi P< 0·05,soleus P < 0·001, rhomboideus P < 0·05), and Ca2+-ATPase (EC 3.6.1.38) concentration was significantly reduced in the two slow-twitch muscles: by 22% in rhomboideus (P < 0·001) and 23% in soleus (P < 0·05). It is concluded that during early postnatal development of large mammals a period of mild hypothyroidism, comparable with that found during undernutrition, induces changes in myofibre differentiation and a down-regulation of cation pumps in skeletal muscle. Such changes would result in slowness of movement and muscle weakness, and also reduce ATP hydrolysis with a concomitant improvement in energetic efficiency.A. P. Harrison, D. R. Tivey, T. Clausen, C. Duchamp and M. J. Daunce
Combinatorics and Boson normal ordering: A gentle introduction
We discuss a general combinatorial framework for operator ordering problems
by applying it to the normal ordering of the powers and exponential of the
boson number operator. The solution of the problem is given in terms of Bell
and Stirling numbers enumerating partitions of a set. This framework reveals
several inherent relations between ordering problems and combinatorial objects,
and displays the analytical background to Wick's theorem. The methodology can
be straightforwardly generalized from the simple example given herein to a wide
class of operators.Comment: 8 pages, 1 figur
Hierarchical Dobinski-type relations via substitution and the moment problem
We consider the transformation properties of integer sequences arising from
the normal ordering of exponentiated boson ([a,a*]=1) monomials of the form
exp(x (a*)^r a), r=1,2,..., under the composition of their exponential
generating functions (egf). They turn out to be of Sheffer-type. We demonstrate
that two key properties of these sequences remain preserved under
substitutional composition: (a)the property of being the solution of the
Stieltjes moment problem; and (b) the representation of these sequences through
infinite series (Dobinski-type relations). We present a number of examples of
such composition satisfying properties (a) and (b). We obtain new Dobinski-type
formulas and solve the associated moment problem for several hierarchically
defined combinatorial families of sequences.Comment: 14 pages, 31 reference
Post-Socialist Self-Censorship:Russia, Hungary and Latvia
This article argues that today in Central and Eastern Europe self-censorship, journalistic freedom and autonomy are just as severely affected by economic constraints, oligarchic influences and new authoritarianism as they are by their Communist pasts. Either way, journalists know exactly what to report, what to omit and how to advance their careers. This is reminiscent of adekvatnost’; a distinct strategy employed by Russian journalists, who regard this skill as an expression of professionalism. It implies having a ‘feel for the game’ and the ‘right instinct’, which allows them to enjoy a certain level of freedom in their work and express their creativity. The authors’ interviews with Latvian and Hungarian journalists, editors and producers examined the extent to which adekvatnost’ might be a feature of journalism beyond Russia, in particular when a media system faces rising populism and authoritarianism, paired with oligarch-dominated ownership. As such, knowledge gained about journalistic practices in the countries under investigation might also be useful in understanding media development beyond the post-Communist space, including Western Europe
Operando analysis of a solid oxide fuel cell by environmental transmission electron microscopy
Correlating the microstructure of an energy conversion device to its
performance is often a complex exercise, notably in solid oxide fuel cell
(SOFC) research. SOFCs combine multiple materials and interfaces that evolve in
time due to high operating temperatures and reactive atmospheres. We
demonstrate here that operando environmental transmission electron microscopy
can simplify the identification of structure-property links in such systems. By
contacting a cathode-electrolyte-anode cell to a heating and biasing
microelectromechanical system in a single-chamber configuration, a direct
correlation is found between the environmental conditions (O2 and H2 partial
pressures, temperature), the cell voltage, and the microstructural evolution of
the fuel cell, down to the atomic scale. The results shed new insights into the
impact of the anode oxidation state and its morphology on the cell electrical
properties.Comment: 18 pages, 5 figure
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