9,974 research outputs found
The future (?) of effective protection
This paper aims at a comparative reading of some archaeological remains in the island of Sardinia, starting from a reflection on the UNESCO discipline, which introduces a hierarchy of cultural heritage based on the level of worthiness of protection and provides enhanced protection for the goods that are on its list. The main goal of the study is to investigate in parallel the application of this ‘selective appreciation’ on the actual context of the protection of the so-called ‘real cultural heritage’ (article 9 of the Italian Constitution). The study proceeds by comparing some important sites on the island having similar contextualization, but different strategies for protection: the Archaeological Park of Porto Torres, Su Nuraxi in Barumini, registered since 1997 in the World Heritage List of UNESCO, and the archaeological area of Neapolis (Oristano). From comparisons and analysis carried out in selected areas it was possible to focus attention on some critical aspects of the UNESCO rules and on contradictions between the operational guidelines and the objectives that the organization provides for the protection of property. In the wake of new reforms for the reorganization of the Ministry of Heritage, Culture and Tourism, the critical issues discussed in this paper appear even more evident in Sardinia. The idea of a ‘protection of the exceptional’ appears to reduce the opportunities of intervention, by isolating the evidence from its context and making the action of protection inadequate for the territory and for the same items contained therein
The future (?) of effective protection
This paper aims at a comparative reading of some archaeological remains in the island of Sardinia, starting from a reflection on the UNESCO discipline, which introduces a hierarchy of cultural heritage based on the level of worthiness of protection and provides enhanced protection for the goods that are on its list. The main goal of the study is to investigate in parallel the application of this ‘selective appreciation’ on the actual context of the protection of the so-called ‘real cultural heritage’ (article 9 of the Italian Constitution). The study proceeds by comparing some important sites on the island having similar contextualization, but different strategies for protection: the Archaeological Park of Porto Torres, Su Nuraxi in Barumini, registered since 1997 in the World Heritage List of UNESCO, and the archaeological area of Neapolis (Oristano). From comparisons and analysis carried out in selected areas it was possible to focus attention on some critical aspects of the UNESCO rules and on contradictions between the operational guidelines and the objectives that the organization provides for the protection of property. In the wake of new reforms for the reorganization of the Ministry of Heritage, Culture and Tourism, the critical issues discussed in this paper appear even more evident in Sardinia. The idea of a ‘protection of the exceptional’ appears to reduce the opportunities of intervention, by isolating the evidence from its context and making the action of protection inadequate for the territory and for the same items contained therein
Many-nodes/many-links spinfoam: the homogeneous and isotropic case
I compute the Lorentzian EPRL/FK/KKL spinfoam vertex amplitude for regular
graphs, with an arbitrary number of links and nodes, and coherent states peaked
on a homogeneous and isotropic geometry. This form of the amplitude can be
applied for example to a dipole with an arbitrary number of links or to the
4-simplex given by the compete graph on 5 nodes. All the resulting amplitudes
have the same support, independently of the graph used, in the large j (large
volume) limit. This implies that they all yield the Friedmann equation: I show
this in the presence of the cosmological constant. This result indicates that
in the semiclassical limit quantum corrections in spinfoam cosmology do not
come from just refining the graph, but rather from relaxing the large j limit.Comment: 8 pages, 4 figure
Compatibility of radial, Lorenz and harmonic gauges
We observe that the radial gauge can be consistently imposed \emph{together}
with the Lorenz gauge in Maxwell theory, and with the harmonic traceless gauge
in linearized general relativity. This simple observation has relevance for
some recent developments in quantum gravity where the radial gauge is
implicitly utilized.Comment: 9 pages, minor changes in the bibliograph
Selection of the Cross-Section Design for the LHC Main Dipole
With the aim of selecting the most suitable design for the series production of the LHC main dipoles, several possible configurations were analysed with respect to admissible component tolerances and structural stability, field level, field quality, number and weight of parts. Two alternatives designs, featuring common collars made out of aluminium alloy and austenitic steel, respectively, were finally compared in detail. Although both designs are almost equivalent at nominal conditions, the austenitic steel collar structure turned out to be far less sensitive to components dimensional variations. This paper reports the main results of the above evaluations, which lead to the choice of austenitic steel collars for the LHC main dipoles
Spinfoams in the holomorphic representation
We study a holomorphic representation for spinfoams. The representation is
obtained via the Ashtekar-Lewandowski-Marolf-Mour\~ao-Thiemann coherent state
transform. We derive the expression of the 4d spinfoam vertex for Euclidean and
for Lorentzian gravity in the holomorphic representation. The advantage of this
representation rests on the fact that the variables used have a clear
interpretation in terms of a classical intrinsic and extrinsic geometry of
space. We show how the peakedness on the extrinsic geometry selects a single
exponential of the Regge action in the semiclassical large-scale asymptotics of
the spinfoam vertex.Comment: 10 pages, 1 figure, published versio
Euclidean three-point function in loop and perturbative gravity
We compute the leading order of the three-point function in loop quantum
gravity, using the vertex expansion of the Euclidean version of the new spin
foam dynamics, in the region of gamma<1. We find results consistent with Regge
calculus in the limit gamma->0 and j->infinity. We also compute the tree-level
three-point function of perturbative quantum general relativity in position
space, and discuss the possibility of directly comparing the two results.Comment: 16 page
Physical boundary state for the quantum tetrahedron
We consider stability under evolution as a criterion to select a physical
boundary state for the spinfoam formalism. As an example, we apply it to the
simplest spinfoam defined by a single quantum tetrahedron and solve the
associated eigenvalue problem at leading order in the large spin limit. We show
that this fixes uniquely the free parameters entering the boundary state.
Remarkably, the state obtained this way gives a correlation between edges which
runs at leading order with the inverse distance between the edges, in agreement
with the linearized continuum theory. Finally, we give an argument why this
correlator represents the propagation of a pure gauge, consistently with the
absence of physical degrees of freedom in 3d general relativity.Comment: 20 pages, 6 figure
Asymptotics of Spinfoam Amplitude on Simplicial Manifold: Euclidean Theory
We study the large-j asymptotics of the Euclidean EPRL/FK spin foam amplitude
on a 4d simplicial complex with arbitrary number of simplices. We show that for
a critical configuration (j_f, g_{ve}, n_{ef}) in general, there exists a
partition of the simplicial complex into three regions: Non-degenerate region,
Type-A degenerate region and Type-B degenerate region. On both the
non-degenerate and Type-A degenerate regions, the critical configuration
implies a non-degenerate Euclidean geometry, while on the Type-B degenerate
region, the critical configuration implies a vector geometry. Furthermore we
can split the Non-degenerate and Type-A regions into sub-complexes according to
the sign of Euclidean oriented 4-simplex volume. On each sub-complex, the spin
foam amplitude at critical configuration gives a Regge action that contains a
sign factor sgn(V_4(v)) of the oriented 4-simplices volume. Therefore the Regge
action reproduced here can be viewed as a discretized Palatini action with
on-shell connection. The asymptotic formula of the spin foam amplitude is given
by a sum of the amplitudes evaluated at all possible critical configurations,
which are the products of the amplitudes associated to different type of
geometries.Comment: 27 pages, 5 figures, references adde
Second-order amplitudes in loop quantum gravity
We explore some second-order amplitudes in loop quantum gravity. In
particular, we compute some second-order contributions to diagonal components
of the graviton propagator in the large distance limit, using the old version
of the Barrett-Crane vertex amplitude. We illustrate the geometry associated to
these terms. We find some peculiar phenomena in the large distance behavior of
these amplitudes, related with the geometry of the generalized triangulations
dual to the Feynman graphs of the corresponding group field theory. In
particular, we point out a possible further difficulty with the old
Barrett-Crane vertex: it appears to lead to flatness instead of Ricci-flatness,
at least in some situations. The observation raises the question whether this
difficulty remains with the new version of the vertex.Comment: 22 pages, 18 figure
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