2,897 research outputs found
in: Morganti R., Zordan M., Museo Guardi Piombino
No full textIl complesso sistema di conoscenze alla base del dispositivo museale - dalla collezione al luogo destinato ad accoglierla, dalle tecniche di allestimento al ruolo del visitatore, permette a Boschi la realizzazione di un progetto interamente giocato su toni discreti volti a coniugare le diverse esperienze di cui è ricca la sua formazione di architetto
Esperienze finalizzate alla gestione conservativa dei boschi di faggio in Sicilia
No full textCon riferimento ai boschi di faggio del Parco naturale dei Nebrodi, in Sicilia, vengono esposti i risultati di un particolare intervento di conversione di un ceduo in fustaia. Il metodo prescelto è quello della matricinatura intensiva con rilascio del materiale di risulta triturato sul posto
New images of the Earth's upper mantle from measurements of surface wave phase velocity anomalies
No full text[1] The sensitivity of a surface wave to the lateral structure of the Earth's mantle depends on the local structure and thickness of the crust; particularly at short periods, the strong lateral heterogeneity of the crust has a significant nonlinear effect on the surface wave "sensitivity functions.'' Thus far, this effect has not been quantified, and tomographic studies of the upper mantle based on surface wave observations have not taken it into account. On the basis of a Jeffreys-Wentzel-Kramers-Brillouin (JWKB) description of surface wave propagation we find and discuss the lateral variations of the sensitivity of Love and Rayleigh waves to mantle seismic anomalies, associated with a realistic model of the crust [Mooney et al., 1998]. We then use the resulting laterally varying sensitivity kernels to determine a new tomographic image of horizontally and vertically polarized shear velocity in the upper mantle from Love and Rayleigh wave phase velocity measurements (periods from 35 to 300 s). In terms of large-scale patterns of high and low velocity our model is similar to previously published ones, confirming, among other features, the anomalous anisotropy underlying the central Pacific [Ekstrom and Dziewonski, 1998]; we find, however, that the lateral dependence of the surface wave sensitivity kernels has a significant effect on the absolute amplitude of the anomalies, which should not be neglected as we attempt to obtain higher-resolution images of the upper mantle
in: Gamba R., Recensioni - Tramezzi urbani
No full textrecensione del volume Fenomenologia della facciat
in: Gamba R., Recensioni - Misericordia, carità, virtù
No full textRecensione del volume Ri-scritture/Re-writing
Measures of resolution in global body wave tomography
No full text[1] The resolution of tomographic images is most often evaluated through synthetic tests: the inversion algorithm used to derive the image itself is applied to a synthetic data set having the same source-station geometry of the real one, but theoretical travel times computed from a chosen "input model'' (e.g., a checkerboard). The similarity between input model and solution of the synthetic test, used as a measure of resolution, has the major shortcoming of depending on the choice of the input model. Conversely, the similarity of the "model resolution matrix'' (R) to the identity matrix is a rigorous measure of resolution that does not depend on any input model, but has the drawback of being computationally heavy. In the past decade, several authors have devised complicated algorithms for the approximate or iterative derivation of R. I show here that parallel Cholesky factorization of A(T) . A ( A being the matrix that identifies the linear inverse problem), feasible on shared-memory multiprocessor servers, provides an efficient way of determining both least squares solutions and resolution matrices in global tomography. I apply this procedure in an evaluation of the resolution of mantle structure from a global P-wave travel time data set
in: De Ciechi R., in Libri Web & App - Ipogeo
No full textRecensione del volume Filosofia del nascost
Long-term rotation and mantle dynamics of the Earth, Mars, and Venus
No full textIn response to internal and surface tectonic processes the terrestrial planets have the ability to displace the axis of rotation with respect to the mantle. This behavior is quantified by means of a nondimensional number, defined here as the rotational number Ro, that allows classification of the planets into two categories, the first containing Mars and the Earth, where true polar wander is a feasible mechanism, and the second, to which Venus belongs, where rotation equilibrium is attained by means of mega-wobbles driven by internal mass anomalies. The number Ro is related to the timescale characterizing the readjustment of the equatorial bulge during long-term polar motion and to the length of the sidereal day. If these two timescales are well separated, the planet experiences true polar wander. Nonlinear Liouville equations for stratified viscoelastic bodies with linear Maxwell rheology are solved in order to assess the relevance of surface and mantle processes in driving long-term rotation instabilities in the terrestrial planets. The amount of true polar wander estimated for the Earth and Mars is reproduced correctly by our modeling with mantle viscosities and lithospheric thickness consistent with other studies. The major difference between the Earth and Mars is the driving mechanism, subduction for the Earth and lithospheric loading for Mars. When mantle viscosities similar to those of the Earth are considered for Venus, the most updated estimate for the offset of about 0.5° between the rotation axis and the axis of maximum inertia is well reproduced during the mega-wobbles induced by internal mass redistribution. We show that the degree 2 topography of these three planets can be affected by their rotation, which is responsible for the dominance of the sectorial component on the Earth and Mars and for the zonal component on Venus
Fluxional behavior of allylpalladium(II) derivatives of N,N'-diarylformamidines and 1,3-diaryltriazenes
No full textReactions of allylpalladium chloride dimer with neutral ligands (L = RN:CHNHR, R = PhCH2, p-MeC6H4, p-ClC6H4; L =
RN:NHR, R = p-MeC6H4, p-ClC6H4) afford bridge splitting products PdClL(1,3--C3H5). Variable temp. 1H and 13C
NMR spectra show 2 dynamic processes in soln. The first one, operating at room temp., involves the dissocn. of the
neutral ligand L; the second one, which has a lower activation energy, is concn. dependent and involves chloride-L
exchange, probably via a pentacoordinated chloro bridge species. The influence of the basicity of the ligands on the
activation energies of the processes is discussed
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