A survey of recommender systems in Twitter

National Research Foundation (NRF) Singapore under International Research Centres in Singapore Funding Initiativ

An architecture for personalized systems based on web mining agents

[EN]The development of the present web systems is becoming a complex activity due to the need to integrate the last technologies in order to make more efficient and competitive applications. Endowing systems with personalized recommendation procedures contributes to achieve these objectives. In this paper, a web mining method for personalization is proposed. It uses the information already available from other users to discover patterns that are used later for making recommendations. The work deals with the problem of introducing new information items and new users who do not have a profile. We propose an architectural design of intelligent data mining agents for the system implementation

Global Strings in High Density QCD

We show that several types of global strings occur in colour superconducting quark matter due to the spontaneous violation of relevant U(1) symmetries. These include the baryon U(1)_B, and approximate axial U(1)_A symmetries as well as an approximate U(1)_S arising from kaon condensation. We discuss some general properties of these strings and their interactions. In particular, we demonstrate that the U(1)_A strings behave as superconducting strings. We draw some parallels between these strings and global cosmological strings and discuss some possible implications of these strings to the physics in neutron star cores.Comment: LaTeX JHEP-format (26 pages) Option in source for REVTeX4 forma

Numerical Portrait of a Relativistic BCS Gapped Superfluid

We present results of numerical simulations of the 3+1 dimensional Nambu - Jona-Lasinio (NJL) model with a non-zero baryon density enforced via the introduction of a chemical potential mu not equal to 0. The triviality of the model with a number of dimensions d>=4 is dealt with by fitting low energy constants, calculated analytically in the large number of colors (Hartree) limit, to phenomenological values. Non-perturbative measurements of local order parameters for superfluidity and their related susceptibilities show that, in contrast to the 2+1 dimensional model, the ground-state at high chemical potential and low temperature is that of a traditional BCS superfluid. This conclusion is supported by the direct observation of a gap in the dispersion relation for 0.5<=(mu a)<=0.85, which at (mu a)=0.8 is found to be roughly 15% the size of the vacuum fermion mass. We also present results of an initial investigation of the stability of the BCS phase against thermal fluctuations. Finally, we discuss the effect of splitting the Fermi surfaces of the pairing partners by the introduction of a non-zero isospin chemical potential.Comment: 41 pages, 19 figures, uses axodraw.sty, v2: minor typographical correction

The strong coupling constant at small momentum as an instanton detector

We present a study of $\alpha_{MOM}(p)$ at small p computed from the lattice. It shows a dramatic $\propto p^4$ law which can be understood within an instanton liquid model. In this framework the prefactor gives a direct measure of the instanton density in thermalised configurations. A preliminary result for this density is 5.27(4) fm^{-4}.Comment: 12 pages, 4 figure

Spectral fluctuation properties of spherical nuclei

The spectral fluctuation properties of spherical nuclei are considered by use of NNSD statistic. With employing a generalized Brody distribution included Poisson, GOE and GUE limits and also MLE technique, the chaoticity parameters are estimated for sequences prepared by all the available empirical data. The ML-based estimated values and also KLD measures propose a non regular dynamic. Also, spherical odd-mass nuclei in the mass region, exhibit a slight deviation to the GUE spectral statistics rather than the GOE.Comment: 10 pages, 2 figure

Effects of T- and P-odd weak nucleon interaction in nuclei: renormalizations due to residual strong interaction, matrix elements between compound states and their correlations with P-violating matrix elements

Manifestations of P-,T-odd weak interaction between nucleons in nucleus are considered. Renormalization of this interaction due to residual strong interaction is studied. Mean squared matrix elements of P-,T-odd weak interaction between compound states are calculated. Correlators between P-,T-odd and P-odd, T-even weak interaction matrix elements between compound states are considered and estimates for these quantities are obtained.Comment: Submitted to Phys. Rev. C; 21 pages, REVTEX 3, no figure

Pion condensation in a dense neutrino gas

We argue that using an equilibrated gas of neutrinos it is possible to probe the phase diagram of QCD for finite isospin and small baryon chemical potentials. We discuss this region of the phase diagram in detail and demonstrate that for large enough neutrino densities a Bose-Einstein condensate of positively charged pions arises. Moreover, we show that for nonzero neutrino density the degeneracy in the lifetimes and masses of the charged pions is lifted.Comment: 10 pages, 7 figures. Modifications to Section II, IIIc, and I