59,644 research outputs found
Fronts, Domain Growth and Dynamical Scaling in a d=1 non-Potential System
We present a study of dynamical scaling and front motion in a one dimensional
system that describes Rayleigh-Benard convection in a rotating cell. We use a
model of three competing modes proposed by Busse and Heikes to which spatial
dependent terms have been added. As long as the angular velocity is different
from zero, there is no known Lyapunov potential for the dynamics of the system.
As a consequence the system follows a non-relaxational dynamics and the
asymptotic state can not be associated with a final equilibrium state. When the
rotation angular velocity is greater than some critical value, the system
undergoes the Kuppers-Lortz instability leading to a time dependent chaotic
dynamics and there is no coarsening beyond this instability. We have focused on
the transient dynamics below this instability, where the dynamics is still
non-relaxational. In this regime the dynamics is governed by a non-relaxational
motion of fronts separating dynamically equivalent homogeneous states. We
classify the families of fronts that occur in the dynamics, and calculate their
shape and velocity. We have found that a scaling description of the coarsening
process is still valid as in the potential case. The growth law is nearly
logarithmic with time for short times and becomes linear after a crossover,
whose width is determined by the strength of the non-potential terms.Comment: 15 pages, 10 figure
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
A framework for closed-loop supply chains of reusable articles
Reuse practices contribute to the environmental and economical sustainability of production and distribution systems. Surprisingly, reuse closed-loop supply chains (CLSC) have not been widely researched for the moment. In this paper, we explore the scientific literature on reuse and we propose a framework for reusable articles. This conceptual structure includes a typology integrating under the reusable articles term different categories of articles (transportation items, packaging materials, tools) and addresses the management issues that arise in reuse CLSC. We ground our results in a set of case studies developed in real industrial settings, which have also been contrasted with cases available in existing literature.reverse logistics;case studies;closed-loop supply chains;returns managment
The distribution of stars around the Milky Way's central black hole II: Diffuse light from sub-giants and dwarfs
This is the second of three papers that search for the predicted stellar cusp
around the Milky Way's central black hole, Sagittarius A*, with new data and
methods. We aim to infer the distribution of the faintest stellar population
currently accessible through observations around Sagittarius A*. We use
adaptive optics assisted high angular resolution images obtained with the NACO
instrument at the ESO VLT. Through optimised PSF fitting we remove the light
from all detected stars above a given magnitude limit. Subsequently we analyse
the remaining, diffuse light density. The analysed diffuse light arises from
sub-giant and main-sequence stars with KS ~ 19 - 20 with masses of 1 - 2 Msol .
These stars can be old enough to be dynamically relaxed. The observed power-law
profile and its slope are consistent with the existence of a relaxed stellar
cusp around the Milky Way's central black hole. We find that a Nuker law
provides an adequate description of the nuclear cluster's intrinsic shape
(assuming spherical symmetry). The 3D power-law slope near Sgr A* is \gamma =
1.23 +- 0.05. At a distance of 0.01 pc from the black hole, we estimate a
stellar mass density of 2.3 +- 0.3 x 10^7 Msol pc^-3 and a total enclosed
stellar mass of 180 +- 20 Msol. These estimates assume a constant mass-to-light
ratio and do not take stellar remnants into account. The fact that no cusp is
observed for bright (Ks 16) giant stars at projected distances of roughly
0.1-0.3 pc implies that some mechanism has altered their appearance or
distribution.Comment: Accepted for publication A&
The distribution of old stars around the Milky Way's central black hole I: Star counts
(abridged) In this paper we revisit the problem of inferring the innermost
structure of the Milky Way's nuclear star cluster via star counts, to clarify
whether it displays a core or a cusp around the central black hole. Through
image stacking and improved PSF fitting we push the completeness limit about
one magnitude deeper than in previous, comparable work. Contrary to previous
work, we analyse the stellar density in well-defined magnitude ranges in order
to be able to constrain stellar masses and ages. The RC and brighter giant
stars display a core-like surface density profile within a projected radius
R<0.3 pc of the central black hole, in agreement with previous studies, but
show a cusp-like surface density distribution at larger R. The surface density
of the fainter stars can be described well by a single power-law at R<2 pc. The
cusp-like profile of the faint stars persists even if we take into account the
possible contamination of stars in this brightness range by young pre-main
sequence stars. The data are inconsistent with a core-profile for the faint
stars.Finally, we show that a 3D Nuker law provides a very good description of
the cluster structure. We conclude that the observed stellar density at the
Galactic Centre, as it can be inferred with current instruments, is consistent
with the existence of a stellar cusp around the Milky Way's central black hole,
Sgr A*. This cusp is well developed inside the influence radius of about 3 pc
of Sgr A* and can be described by a single three-dimensional power-law with an
exponent gamma=1.23+-0.05. The apparent lack of RC stars and brighter giants at
projected distances of R < 0.3 pc (R<8") of the massive black hole may indicate
that some mechanism has altered their distribution or intrinsic luminosity.Comment: Accepted for publication A&
Channel Blockade in a Two-Path Triple-Quantum-Dot System
Electronic transport through a two-path triple-quantum-dot system with two
source leads and one drain is studied. By separating the conductance of the two
double dot paths, we are able to observe double dot and triple dot physics in
transport and study the interaction between the paths. We observe channel
blockade as a result of inter-channel Coulomb interaction. The experimental
results are understood with the help of a theoretical model which calculates
the parameters of the system, the stability regions of each state and the full
dynamical transport in the triple dot resonances.Comment: 6 pages, 6 figure
Work and entropy production in generalised Gibbs ensembles
Recent years have seen an enormously revived interest in the study of
thermodynamic notions in the quantum regime. This applies both to the study of
notions of work extraction in thermal machines in the quantum regime, as well
as to questions of equilibration and thermalisation of interacting quantum
many-body systems as such. In this work we bring together these two lines of
research by studying work extraction in a closed system that undergoes a
sequence of quenches and equilibration steps concomitant with free evolutions.
In this way, we incorporate an important insight from the study of the dynamics
of quantum many body systems: the evolution of closed systems is expected to be
well described, for relevant observables and most times, by a suitable
equilibrium state. We will consider three kinds of equilibration, namely to (i)
the time averaged state, (ii) the Gibbs ensemble and (iii) the generalised
Gibbs ensemble (GGE), reflecting further constants of motion in integrable
models. For each effective description, we investigate notions of entropy
production, the validity of the minimal work principle and properties of
optimal work extraction protocols. While we keep the discussion general, much
room is dedicated to the discussion of paradigmatic non-interacting fermionic
quantum many-body systems, for which we identify significant differences with
respect to the role of the minimal work principle. Our work not only has
implications for experiments with cold atoms, but also can be viewed as
suggesting a mindset for quantum thermodynamics where the role of the external
heat baths is instead played by the system itself, with its internal degrees of
freedom bringing coarse-grained observables to equilibrium.Comment: 22 pages, 4 figures, improvements in presentatio
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