86,591 research outputs found
Il processo di trasformazione della comunità locale:struttura sociale, valori e nuovi percorsi della politica sociale
No full textFirst order phase transitions in cosmology
No full textWe review the observable effects produced by phase transitions occurring along with inflation. Firstly, we present a model which is able to generate a locally open universe as the result of a very early phase transition peaked at a precise epoch. Then, we show how the same model can produce primordial voids on the large scale structure, able to imprint in an observable way the microwave background. Finally, we speculate on the possibility of merging the two mechanisms in the same process
Reconciling inflation with openness
No full textIt is already understood that the increasing observational evidence for an open universe can be reconciled with inflation if our horizon is contained inside one single huge bubble nucleated during the inflationary phase transition. In this frame of ideas, we show here that the probability of living in a bubble with the right Ω0(≈0.2) can be comparable to unity, rather than infinitesimally small. For this purpose we modify both quantitatively and qualitatively an intuitive toy model of ours. Therefore, inferring from the observations that Ω0<1 not only does not conflict with the inflationary paradigm, but rather supports therein the occurrence of a primordial phase transition
Peaks and Rings on the Cosmic Microwave Background
No full textWe simulate maps of the microwave background radiation for a model of inflationary primordial voids plus standard cold dark matter. For some values of the parameters, we find in the angular power spectrum a well-defined second peak at l~1000, correlated with the size, amplitude, and number of the primordial voids. The next generation of microwave background maps will be able to test the scenario of inflationary first-order phase transitions
Imprints of primordial voids on the cosmic microwave background
No full textWe generalize in several ways the results existing in the literature regarding the interaction between primordial voids and the cosmic microwave background: (a) we make use of an exact general relativistic solution for a spherical, nearly empty cavity in the matter-dominated era to evaluate the null geodesics and the Sachs-Wolfe effect; (b) we evaluate the magnitude of the adiabatic fluctuations of the photon-baryon plasma; (c) we study the influence of the shell profile; and (d) we take into account the finite thickness of the last scattering surface (LSS) and the influence of its position with respect to the void centre. We find empirically an analytic approximation to the Sachs-Wolfe effect for all crossing geometries and we derive an upper limit of ≈ 25 h−1 Mpc for the comoving radii of voids sitting on the LSS in order to achieve compatibility with COBE data. As a nearly empty void has an overcomoving expansion of a factor of ≈ 4 between decoupling and the present, the maximum allowed size at present is ≈ 100 h−1 Mpc. On the other hand, the smallness of the comoving size relative to the sound horizon reduces strongly the adiabatic effect by Silk damping and makes it negligible. Most of the signature of primordial voids comes therefore from metric effects and consists of subdegree spots that are blue or red depending on whether their centre lies beyond or within the LSS. In conclusion we refine and confirm earlier constraints on a power-law void spectrum originating in an inflationary phase transition and capable of generating the observed large-scale structure
Ozonation of thioamide containing heterocycles. A new general and selective procedure for the synthesis of C-2 substituted heteroazole derivatives.
No full text2-Mercaptoheterazoles readily react with ozone in the presence of
nucleophiles and under mild experimental conditions to form several C-2
substituted heterazoles
An unexpected and efficient direct nucleophilic C-4 hydroxy substitution on 2-methoxy- and 2-mrthylthio-4(3H)-pyrimidinones bearing a diethylamino moiety on the C-6 side chain
No full textThe unexpected and efficient direct nucleophilic C-4 hydroxy (oxo) substitution by sodium alkoxides on 2-methoxy- and 2-methylthio-4(3H)- pyrimidinones bearing a diethylamino moiety on the c-6 side chain is reported. An unprecedented tandem C-6 side chain Hofmann-like elimination /C- 4 pyrimidinone substitution is also reported. This provides a good method for the synthesis of new C-6 vinyl cytosine derivatives
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