4,397 research outputs found
Combinatorial formulation of Ising model revisited
In 1952, Kac and Ward developed a combinatorial formulation for the two
dimensional Ising model which is another method of obtaining Onsager's formula
for the free energy per site in the thermodynamic limit of the model. Feynman
gave an important contribution to this formulation conjecturing a crucial
mathematical relation which completed Kac and Ward ideas. In this paper, the
method of Kac, Ward and Feynman for the free field Ising model in two
dimensions is reviewed in a selfcontained way.Comment: 27 pages, 17 figure
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Ethics and Design in the Brazilian Context
Often driven by practical and immediate requirements, more and more people are incorporating technology into a variety of aspects of their lives, often without reflecting on the consequences of using them. On the other hand, studies on interactive system development that lead to behavioral change have been gaining ground on the agenda of large HCI conferences. This movement brings to the forefront the fundamental issues of ethics in design and technology use. A designer’s intentions, when directing certain actions or behaviors, are not always explicit or desired by the stakeholders affected by the use of the technology. Systems that induce an undesired purchase, or even those that use conditioning strategies to cause a behavioral change are examples of such intentions. The challenge proposed is therefore about the relationship between design and personal freedom in a way that these technology users do not become victims, either passively or submissively, of the effects of its use. This advance allows for the redefinition of the relationship between man and technology, and the application of new forms of designing and developing interactive systems that take into account the ethical aspects of this relationship
Exact Effective action for (1+1)-dimensional fermions in an Abelian background at finite temperature and chemical potential
In this paper we study the effects of a nonzero chemical potential in the
effective action for massless fermions in (1+1) dimensions in an abelian gauge
field background at finite temperature. We calculate the n-point function and
show that the structure of the amplitudes corresponds to a generalization of
the structure noted earlier in a calculation without a chemical potential (the
associated integrals carry the dependence on the chemical potential). Our
calculation shows that the chiral anomaly is unaffected by the presence of a
chemical potential at finite temperature. However, unlike the earlier
calculation (in the absence of a chemical potential) odd point functions do not
vanish. We trace this to the fact that in the presence of a chemical potential
the generalized charge conjugation symmetry of the theory allows for such
amplitudes. In fact, we find that all the even point functions are even
functions of the chemical potential while the odd point functions are odd
functions of it which is consistent with this generalized charge conjugation
symmetry. We show that the origin of the structure of the amplitudes is best
seen from a formulation of the theory in terms of left and right handed
spinors. The calculations are also much simpler in this formulation and it
clarifies many other aspects of the theory
Viable entanglement detection of unknown mixed states in low dimensions
We explore procedures to detect entanglement of unknown mixed states, which
can be experimentally viable. The heart of the method is a hierarchy of simple
feasibility problems, which provides sufficient conditions to entanglement. Our
numerical investigations indicate that the entanglement is detected with a cost
which is much lower than full state tomography. The procedure is applicable to
both free and bound entanglement, and involves only single copy measurements.Comment: 8 pages, 9 figures, 4 table
MATHEMATICAL MODEL AND EXPERIMENTAL PROCEEDINGS TO DETERMINE ROLL WAVES IN OPEN CHANNELS
The goal of this paper is consolidate a representative model previously developed by RMVP team (Rheological Studies on Viscous and Viscousplastic Materials) from UNESP - Ilha Solteira, for a typical phenomenonthat occurs on spillways, river's bed, landslides, mudflows, blood flows, for Newtonian and non-Newtonian fluids, known as roll waves. Another goal of this paper is present an experimental project designed for capturing measurements (amplitude and wavelength) of these instabilities. From a mathematical perspective, a first-order analytical model is showed, based on Cauchy's equations system, once developed by the team (Ferreira, 2007), which provides a generation condition for roll waves through temporal linear stability analysis. This model follows the remarkable work of Dressler (1949) and it is able to generate roll waves for many rheological configurations, from Newtonian to Herschel & Bulkley models, representing clean water up to muddy mixtures, respectively. A numerical routine developed in Matlab/Simulink is used to show some results that illustrate roll waves pattern. Due to the lack of roll waves data (amplitude and wavelength), the team started to focus on the experimental approach of the phenomenon, aiming to design an apparatus that would be capable to reproduce roll waves in special conditions of flow, isolated from external perturbations. This project is here presented along with a proposal of a photometric system to ascertain measures of the flow height through light absorption technique, based on experiments found in the literature. The final execution of this experiment and the correct obtaining of amplitude and wavelength will contribute for the validation of the model here presented
Iron abundances from high-resolution spectroscopy of the open clusters NGC 2506, NGC 6134, and IC 4651
This is the first of a series of papers devoted to derive the metallicity of
old open clusters in order to study the time evolution of the chemical
abundance gradient in the Galactic disk. We present detailed iron abundances
from high resolution (R~40000) spectra of several red clump and bright giant
stars in the open clusters IC 4651, NGC 2506 and NGC 6134. We observed 4 stars
of NGC 2506, 3 stars of NGC 6134, and 5 stars of IC 4651 with the FEROS
spectrograph at the ESO 1.5 m telescope; moreover, 3 other stars of NGC 6134
were observed with the UVES spectrograph on Kueyen (VLT UT2). After excluding
the cool giants near the red giant branch tip (one in IC 4651 and one in NGC
2506), we found overall [Fe/H] values of -0.20 +/- 0.01, rms = 0.02 dex (2
stars) for NGC 2506, +0.15 +/- 0.03, rms = 0.07 dex (6 stars) for NGC 6134, and
+0.11 +/- 0.01, rms = 0.01 dex (4 stars) for IC 4651. The metal abundances
derived from line analysis for each star were extensively checked using
spectrum synthesis of about 30 to 40 Fe I lines and 6 Fe II lines. Our
spectroscopic temperatures provide reddening values in good agreement with
literature data for these clusters, strengthening the reliability of the
adopted temperature and metallicity scale. Also, gravities from the Fe
equilibrium of ionization agree quite well with expectations based on cluster
distance moduli and evolutionary masses.Comment: 13 pages, 7 figures, uses aa.cls, accepted for publication on
Astronomy & Astrophysic
Coherent structures in a non-equilibrium large-velocity-defect turbulent boundary layer
The characteristics of the coherent structures in a strongly decelerated largevelocity-defect
boundary layer are analysed by direct numerical simulation. The simulated
boundary layer starts as a zero-pressure-gradient boundary layer, decelerates under a strong
adverse pressure gradient, and separates near the end of the domain, in the form of a
very thin separation bubble. The Reynolds number at separation is Re¿ = 3912 and the
shape factor H = 3.43. The three-dimensional spatial correlations of (u, u) and (u, v) are
investigated and compared to those of a zero-pressure-gradient boundary layer and another
strongly decelerated boundary layer. These velocity pairs lose coherence in the streamwise
and spanwise directions as the velocity defect increases. In the outer region, the shape of
the correlations suggest that large-scale u structures are less streamwise elongated and more
inclined with respect to the wall in large-defect boundary layers. The three-dimensional
properties of sweeps and ejections are characterized for the first time in both the zeropressure-gradient
and adverse-pressure-gradient boundary layers, following the method of
Lozano-Duran et al. (J. Fluid Mech. ´ 694, 100–130, 2012). Although longer sweeps and
ejections are found in the zero-pressure-gradient boundary layer, with ejections reaching
streamwise lengths of 5 boundary layer thicknesses, the sweeps and ejections tend to be
bigger in the adverse-pressure-gradient boundary layer. Moreover, small near-wall sweeps
and ejections are much less numerous in the large-defect boundary layer. Large sweeps and
ejections that reach the wall region (wall-attached) are also less numerous, less streamwise
elongated and they occupy less space than in the zero-pressure-gradient boundary layer
Energy transfer mechanisms in adverse pressure gradient turbulent boundary layers
The energy transfer mechanisms and structures playing a role in these
mechanisms in adverse-pressure-gradient (APG) turbulent boundary layers (TBLs)
with small and large velocity defects are investigated. We examine the
wall-normal and spectral distributions of energy, production and
pressure-strain in APG TBLs and compare these distributions with those in
canonical flows. It is found that the spectral distributions of production and
pressure-strain are not profoundly affected by an increase of the velocity
defect, although the energy spectra drastically change in the inner layer of
the large defect APG TBL. In the latter, the signature of the inner layer
streaks is absent from the energy spectra. However, the production and
pressure-strain spectra suggest that the near-wall cycle or another energy
transfer mechanism with similar spectral features still exist in large defect
TBLs. In the outer layer, energetic, production and pressure-strain structures
appear to change from wall-attached to wall-detached structures with increasing
velocity defect. Despite this, the 2D spectral distributions have similar
shapes and wavelength aspect ratios of the peaks in all these flows. These
observations suggest that outer layer energy transfer mechanisms may be the
same in wall-bounded flows, no matter if dynamically relevant structures are
attached or detached to the wall. Therefore, the conclusion is that the
mechanisms responsible for turbulence production and inter-component energy
transfer may remain the same within each layer in all these flows. It is the
intensity of these mechanisms within one layer that changes with velocity
defect, because of the local mean shear variation
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