RECERCAT - Articles publicats en revistes (Estructura i Constituents de la Matèria)
http://www.recercat.cat:80/handle/2072/48808
www.ub.eduTue, 30 Sep 2014 16:03:35 GMT2014-09-30T16:03:35ZThe Channel Imagehttp://www.recercat.cat:80/bitstream/id/26376/
http://www.recercat.cat:80/handle/2072/48808
Symmetry coefficients and incompressibility of clusterized supernova matter
http://www.recercat.cat:80/handle/2072/217254
Symmetry coefficients and incompressibility of clusterized supernova matter
Samaddar, S. K.; De, J. N.; Viñas Gausí, Xavier; Centelles Aixalà, Mario
The symmetry energy coefficients, incompressibility, and single-particle and isovector potentials of clusterized dilute nuclear matter are calculated at different temperatures employing the S-matrix approach to the evaluation of the equation of state. Calculations have been extended to understand the aforesaid properties of homogeneous and clusterized supernova matter in the subnuclear density region. A comparison of the results in the S-matrix and mean-field approach reveals some subtle differences in the density and temperature region we explore.
http://www.recercat.cat:80/handle/2072/217254Asymmetric stochastic switching driven by intrinsic molecular noise
http://www.recercat.cat:80/handle/2072/227133
Asymmetric stochastic switching driven by intrinsic molecular noise
Frigola, David; Casanellas Vilageliu, Laura; Sancho, José M.; Ibañes Miguez, Marta
Low-copy-number molecules are involved in many functions in cells. The intrinsic fluctuations of these numbers can enable stochastic switching between multiple steady states, inducing phenotypic variability. Herein we present a theoretical and computational study based on Master Equations and Fokker-Planck and Langevin descriptions of stochastic switching for a genetic circuit of autoactivation. We show that in this circuit the intrinsic fluctuations arising from low-copy numbers, which are inherently state-dependent, drive asymmetric switching. These theoretical results are consistent with experimental data that have been reported for the bistable system of the gallactose signaling network in yeast. Our study unravels that intrinsic fluctuations, while not required to describe bistability, are fundamental to understand stochastic switching and the dynamical relative stability of multiple states.
http://www.recercat.cat:80/handle/2072/227133Nuclear expansion with excitation
http://www.recercat.cat:80/handle/2072/217280
Nuclear expansion with excitation
De, J. N.; Samaddar, S. K.; Viñas Gausí, Xavier; Centelles Aixalà, Mario
The expansion of an isolated hot spherical nucleus with excitation energy and its caloric curve are studied in a thermodynamic model with the SkM∗ force as the nuclear effective two-body inter-action. The calculated results are shown to compare well with the recent experimental data from energetic nuclear collisions. The fluctuations in temperature and density are also studied. They are seen to build up very rapidly beyond an excitation energy of ∼9 MeV/u. Volume-conserving quadrupole deformation in addition to expansion indicates , however, nuclear disassembly above an excitation energy of ∼4 MeV/u.
http://www.recercat.cat:80/handle/2072/217280New method for measuring longitudinal fuctuations and directed flow in ultrarelativistic heavy ion reactions
http://www.recercat.cat:80/handle/2072/204984
New method for measuring longitudinal fuctuations and directed flow in ultrarelativistic heavy ion reactions
Csernai, L. P.; Eyyubova, G.; Magas, V. K.
It has been shown in recent ALICE@LHC measurements that the odd flow harmonics, in particular, a directed flow v1, occurred to be weak and dominated by random fluctuations. In this work we propose a new method, which makes the measurements more sensitive to the flow patterns showing global collective symmetries. We demonstrate how the longitudinal center of mass rapidity fluctuations can be identified, and then the collective flow analysis can be performed in the event-by-event center of mass frame. Such a method can be very effective in separating the flow patterns originating from random fluctuations, and the flow patterns originating from the global symmetry of the initial state.
http://www.recercat.cat:80/handle/2072/204984Fluid dynamical prediction of changed v1-flow at energies available at the CERN Large Hadron Collider
http://www.recercat.cat:80/handle/2072/239330
Fluid dynamical prediction of changed v1-flow at energies available at the CERN Large Hadron Collider
Csernai, L. P.; Magas, V. K.; Stöcker, Horst; Strottman, D.
Substantial collective flow is observed in collisions between lead nuclei at Large Hadron Collider (LHC) as evidenced by the azimuthal correlations in the transverse momentum distributions of the produced particles. Our calculations indicate that the global v1-flow, which at RHIC peaked at negative rapidities (named third flow component or antiflow), now at LHC is going to turn toward forward rapidities (to the same side and direction as the projectile residue). Potentially this can provide a sensitive barometer to estimate the pressure and transport properties of the quark-gluon plasma. Our calculations also take into account the initial state center-of-mass rapidity fluctuations, and demonstrate that these are crucial for v1 simulations. In order to better study the transverse momentum flow dependence we suggest a new"symmetrized" vS1(pt) function, and we also propose a new method to disentangle global v1 flow from the contribution generated by the random fluctuations in the initial state. This will enhance the possibilities of studying the collective Global v1 flow both at the STAR Beam Energy Scan program and at LHC.
http://www.recercat.cat:80/handle/2072/239330Bose-Fermi mixtures in optical lattices
http://www.recercat.cat:80/handle/2072/217281
Bose-Fermi mixtures in optical lattices
Centelles Aixalà, Mario; Guilleumas, Montserrat; Barranco Gómez, Manuel; Mayol Sánchez, Ricardo; Pi Pericay, Martí
Using mean field theory, we have studied Bose-Fermi mixtures in a one-dimensional optical lattice in the case of an attractive boson-fermion interaction. We consider that the fermions are in the degenerate regime and that the laser intensities are such that quantum coherence across the condensate is ensured. We discuss the effect of the optical lattice on the critical rotational frequency for vortex line creation in the Bose-Einstein condensate, as well as how it affects the stability of the boson-fermion mixture. A reduction of the critical frequency for nucleating a vortex is observed as the strength of the applied laser is increased. The onset of instability of the mixture occurs for a sizably lower number of fermions in the presence of a deep optical lattice.
http://www.recercat.cat:80/handle/2072/217281Momentum dependence of the phi-meson nuclear transparency
http://www.recercat.cat:80/handle/2072/224409
Momentum dependence of the phi-meson nuclear transparency
Hartmann, M.; Kiselev, Yu. T.; Polyanskiy, A.; Paryev, E. Ya.; Büscher, M.; Chiladze, D.; Dymov, S.; Dzyuba, A.; Gebel, R.; Hejny, V.; Kämpfer, B.; Keshelashvili, I.; Koptev, V.; Lorentz, B.; Maeda, Y.; Magas, V. K.; Merzliakov, S.; Mikirtytchiants, S.; Nekipelov, M.; Ohm, H.
The production of φ mesons in proton collisions with C, Cu, Ag, and Au targets has been studied via the φ → K + K − decay at an incident beam energy of 2.83 GeV using the ANKE detector system at COSY. For the first time, the momentum dependence of the nuclear transparency ratio, the in-medium φ width, and the differential cross section for φ -meson production at forward angles have been determined for these targets over the momentum range of 0.6-1.6 GeV /c. There are indications of a significant momentum dependence in the value of the extracted φ width, which corresponds to an effective φN absorption cross section in the range of 14-21 mb.
http://www.recercat.cat:80/handle/2072/224409Nuclear Symmetry Energy Probed by Neutron Skin Thickness of Nuclei
http://www.recercat.cat:80/handle/2072/217257
Nuclear Symmetry Energy Probed by Neutron Skin Thickness of Nuclei
Centelles Aixalà, Mario; Roca-Maza, X.; Viñas Gausí, Xavier; Warda, M.
We describe a relation between the symmetry energy coefficients csym(ρ) of nuclear matter and asym(A) of finite nuclei that accommodates other correlations of nuclear properties with the low-density behavior of csym(ρ). Here, we take advantage of this relation to explore the prospects for constraining csym(ρ) of systematic measurements of neutron skin sizes across the mass table, using as example present data from antiprotonic atoms. The found constraints from neutron skins are in harmony with the recent determinations from reactions and giant resonances.
http://www.recercat.cat:80/handle/2072/217257Microscopic-macroscopic approach for binding energies with the Wigner-Kirkwood method
http://www.recercat.cat:80/handle/2072/217253
Microscopic-macroscopic approach for binding energies with the Wigner-Kirkwood method
Bhagwat, A.; Viñas Gausí, Xavier; Centelles Aixalà, Mario; Schuck, Peter; Wyss, R.
The semiclassical Wigner-Kirkwood ̄h expansion method is used to calculate shell corrections for spherical and deformed nuclei. The expansion is carried out up to fourth order in ̄h. A systematic study of Wigner-Kirkwood averaged energies is presented as a function of the deformation degrees of freedom. The shell corrections, along with the pairing energies obtained by using the Lipkin-Nogami scheme, are used in the microscopic-macroscopic approach to calculate binding energies. The macroscopic part is obtained from a liquid drop formula with six adjustable parameters. Considering a set of 367 spherical nuclei, the liquid drop parameters are adjusted to reproduce the experimental binding energies, which yields a root mean square (rms) deviation of 630 keV. It is shown that the proposed approach is indeed promising for the prediction of nuclear masses.
http://www.recercat.cat:80/handle/2072/217253Identification of neuronal network properties from the spectral analysis of calcium imaging signals in neuronal cultures
http://www.recercat.cat:80/handle/2072/238832
Identification of neuronal network properties from the spectral analysis of calcium imaging signals in neuronal cultures
Tibau, Elisenda; Valencia, Miguel; Soriano i Fradera, Jordi
Neuronal networks in vitro are prominent systems to study the development of connections in living neuronal networks and the interplay between connectivity, activity and function. These cultured networks show a rich spontaneous activity that evolves concurrently with the connectivity of the underlying network. In this work we monitor the development of neuronal cultures, and record their activity using calcium fluorescence imaging. We use spectral analysis to characterize global dynamical and structural traits of the neuronal cultures. We first observe that the power spectrum can be used as a signature of the state of the network, for instance when inhibition is active or silent, as well as a measure of the network's connectivity strength. Second, the power spectrum identifies prominent developmental changes in the network such as GABAA switch. And third, the analysis of the spatial distribution of the spectral density, in experiments with a controlled disintegration of the network through CNQX, an AMPA-glutamate receptor antagonist in excitatory neurons, reveals the existence of communities of strongly connected, highly active neurons that display synchronous oscillations. Our work illustrates the interest of spectral analysis for the study of in vitro networks, and its potential use as a network-state indicator, for instance to compare healthy and diseased neuronal networks.
http://www.recercat.cat:80/handle/2072/238832Giant monopole energies from a constrained relativistic mean-field approach
http://www.recercat.cat:80/handle/2072/220110
Giant monopole energies from a constrained relativistic mean-field approach
Chen, Wei-Chia; Piekarewicz, J.; Centelles Aixalà, Mario
Background:Average energies of nuclear collective modes may be efficiently and accurately computed using a nonrelativistic constrained approach without reliance on a random phase approximation (RPA). Purpose: To extend the constrained approach to the relativistic domain and to establish its impact on the calibration of energy density functionals. Methods: Relativistic RPA calculations of the giant monopole resonance (GMR) are compared against the predictions of the corresponding constrained approach using two accurately calibrated energy density functionals. Results: We find excellent agreement at the 2% level or better between the predictions of the relativistic RPA and the corresponding constrained approach for magic (or semimagic) nuclei ranging from 16 O to 208 Pb. Conclusions: An efficient and accurate method is proposed for incorporating nuclear collective excitations into the calibration of future energy density functionals.
http://www.recercat.cat:80/handle/2072/220110Analysis of bulk and surface contributions in the neutron skin of nuclei
http://www.recercat.cat:80/handle/2072/217252
Analysis of bulk and surface contributions in the neutron skin of nuclei
Warda, M.; Viñas Gausí, Xavier; Roca-Maza, X.; Centelles Aixalà, Mario
The neutron skin thickness of nuclei is a sensitive probe of the nuclear symmetry energy and has multiple implications for nuclear and astrophysical studies. However, precision measurements of this observable are difficult to obtain. The analysis of the experimental data may imply some assumptions about the bulk or surface nature of the formation of the neutron skin. Here we study the bulk or surface character of neutron skins of nuclei following from calculations with Gogny, Skyrme, and covariant nuclear mean-field interactions. These interactions are successful in describing nuclear charge radii and binding energies but predict different values for neutron skins. We perform the study by fitting two-parameter Fermi distributions to the calculated self-consistent neutron and proton densities. We note that the equivalent sharp radius is a more suitable reference quantity than the half-density radius parameter of the Fermi distributions to discern between the bulk and surface contributions in neutron skins. We present calculations for nuclei in the stability valley and for the isotopic chains of Sn and Pb.
http://www.recercat.cat:80/handle/2072/217252Nuclear surface properties in relativistic effective field theory
http://www.recercat.cat:80/handle/2072/217307
Nuclear surface properties in relativistic effective field theory
Estal, Manuel del; Centelles Aixalà, Mario; Viñas Gausí, Xavier
We perform Hartree calculations of symmetric and asymmetric semi-infinite nuclear matter in the framework of relativistic models based on effective hadronic field theories as recently proposed in the literature. In addition to the conventional cubic and quartic scalar self-interactions, the extended models incorporate a quartic vector self-interaction, scalar-vector non-linearities and tensor couplings of the vector mesons. We investigate the implications of these terms on nuclear surface properties such as the surface energy coefficient, surface thickness, surface stiffness coefficient, neutron skin thickness and the spin-orbit force.
http://www.recercat.cat:80/handle/2072/217307Langevin equations with multiplicative noise: Application to domain growth
http://www.recercat.cat:80/handle/2072/226985
Langevin equations with multiplicative noise: Application to domain growth
Sancho, José M.; Hernández Machado, Aurora; Ramírez de la Piscina, Laureano; Lacasta Palacio, Ana María
Langevin Equations of Ginzburg-Landau form, with multiplicative noise, are proposed to study the effects of fluctuations in domain growth. These equations are derived from a coarse-grained methodology. The Cahn-Hiliard-Cook linear stability analysis predicts some effects in the transitory regime. We also derive numerical algorithms for the computer simulation of these equations. The numerical results corroborate the analytical predictions of the linear analysis. We also present simulation results for spinodal decomposition at large times.
http://www.recercat.cat:80/handle/2072/226985Incompressibility of neutron-rich matter
http://www.recercat.cat:80/handle/2072/217256
Incompressibility of neutron-rich matter
Piekarewicz, J.; Centelles Aixalà, Mario
The saturation properties of neutron-rich matter are investigated in a relativistic mean-field formalism using two accurately calibrated models: NL3 and FSUGold. The saturation properties density, binding energy per nucleon, and incompressibility coefficient are calculated as a function of the neutron-proton asymmetry α≡(N-Z)/A to all orders in α. Good agreement (at the 10% level or better) is found between these numerical calculations and analytic expansions that are given in terms of a handful of bulk parameters determined at saturation density. Using insights developed from the analytic approach and a general expression for the incompressibility coefficient of infinite neutron-rich matter, i.e., K0(α)=K0+Kτα2+ , we construct a hybrid model with values for K0 and Kτ as suggested by recent experimental findings. Whereas the hybrid model provides a better description of the measured distribution of isoscalar monopole strength in the Sn isotopes relative to both NL3 and FSUGold, it significantly underestimates the distribution of strength in 208Pb. Thus, we conclude that the incompressibility coefficient of neutron-rich matter remains an important open problem.
http://www.recercat.cat:80/handle/2072/217256First measurement of time-dependent CP violation in B0s→K+K− decays
http://www.recercat.cat:80/handle/2072/238350
First measurement of time-dependent CP violation in B0s→K+K− decays
Calvo Gómez, M.; Camboni, Alessandro; Comerma Montells, Albert; Garrido Beltrán, Lluís; Graciani Díaz, Ricardo; Graugés Pous, Eugeni; Oyanguren, A.; Pérez-Calero Yzquierdo, Antonio; Picatoste Olloqui, Eduardo; Potterat, Cédric; Rives Molina, V.; Ruiz, Hugo (Ruiz Pérez); Ruiz Valls, P.; Vilasis-Cardona, X.; LHCb Collaboration
Direct and mixing-induced CP-violating asymmetries in B0s→K+K− decays are measured for the first time using a data sample of pp collisions, corresponding to an integrated luminosity of 1.0 fb−1, collected with the LHCb detector at a centre-of-mass energy of 7 TeV. The results are C KK = 0.14 ± 0.11 ± 0.03 and S KK = 0.30 ± 0.12 ± 0.04, where the first uncertainties are statistical and the second systematic. The corresponding quantities are also determined for B 0 → π + π − decays to be C ππ = −0.38 ± 0.15 ± 0.02 and S ππ = −0.71 ± 0.13 ± 0.02, in good agreement with existing measurements.
http://www.recercat.cat:80/handle/2072/238350Microscopic-macroscopic approach for binding energies with the Wigner-Kirkwood method. II. Deformed nuclei
http://www.recercat.cat:80/handle/2072/217218
Microscopic-macroscopic approach for binding energies with the Wigner-Kirkwood method. II. Deformed nuclei
Bhagwat, A.; Viñas Gausí, Xavier; Centelles Aixalà, Mario; Schuck, Peter; Wyss, R.
The binding energies of deformed even-even nuclei have been analyzed within the framework of a recently proposed microscopic-macroscopic model. We have used the semiclassical Wigner-Kirkwood ̄h expansion up to fourth order, instead of the usual Strutinsky averaging scheme, to compute the shell corrections in a deformed Woods-Saxon potential including the spin-orbit contribution. For a large set of 561 even-even nuclei with Z 8 and N 8, we find an rms deviation from the experiment of 610 keV in binding energies, comparable to the one found for the same set of nuclei using the finite range droplet model of Moller and Nix (656 keV). As applications of our model, we explore its predictive power near the proton and neutron drip lines as well as in the superheavy mass region. Next, we systematically explore the fourth-order Wigner-Kirkwood corrections to the smooth part of the energy. It is found that the ratio of the fourth-order to the second-order corrections behaves in a very regular manner as a function of the asymmetry parameter I=(N−Z)/A. This allows us to absorb the fourth-order corrections into the second-order contributions to the binding energy, which enables us us to simplify and speed up the calculation of deformed nuclei.
http://www.recercat.cat:80/handle/2072/217218Microscopic derivation of a NN*(1440) potential
http://www.recercat.cat:80/handle/2072/210670
Microscopic derivation of a NN*(1440) potential
Juliá-Díaz, Bruno; Fernández, F.; González Cámara, Pablo; Valcarce, A.
We derive a NN*(1440) potential from a nonrelativistic quark-quark interaction and a quark cluster model for the baryons. By making use of the Born-Oppenheimer approximation, we examine quark Pauli correlations in detail. A comparison with the NN potential derived in the same framework is done. This makes it possible to emphasize the role of quark antisymmetry beyond baryon antisymmetry and to discuss the use of phenomenological NN*(1440) baryonic potentials.
http://www.recercat.cat:80/handle/2072/210670First evidence for the two-body charmless baryonic decay
http://www.recercat.cat:80/handle/2072/238351
First evidence for the two-body charmless baryonic decay
LHCb Collaboration; Calvo Gómez, M.; Camboni, Alessandro; Comerma Montells, Albert; Garrido Beltrán, Lluís; Graciani Díaz, Ricardo; Graugés Pous, Eugeni; Oyanguren, A.; Pérez-Calero Yzquierdo, Antonio; Picatoste Olloqui, Eduardo; Potterat, Cédric; Rives Molina, V.; Ruiz, Hugo (Ruiz Pérez); Ruiz Valls, P.; Vilasis-Cardona, X.
The results of a search for the rare two-body charmless baryonic decays TeX and TeX are reported. The analysis uses a data sample, corresponding to an integrated luminosity of 0.9 fb−1, of pp collision data collected by the LHCb experiment at a centre-of-mass energy of 7 TeV. An excess of TeX candidates with respect to background expectations is seen with a statistical significance of 3.3 standard deviations. This is the first evidence for a two-body charmless baryonic B 0 decay. No significant TeX signal is observed, leading to an improvement of three orders of magnitude over previous bounds. If the excess events are interpreted as signal, the 68.3% confidence level intervals on the branching fractions are $ TeX $ where the first uncertainty is statistical and the second is systematic.
http://www.recercat.cat:80/handle/2072/238351Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy
http://www.recercat.cat:80/handle/2072/238743
Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy
Garrido Beltrán, Lluís; Gascón Fora, David; Graciani Díaz, Ricardo; Munar i Adrover, Pere; Paredes i Poy, Josep Maria; Ribó Gomis, Marc; Sanuy Charles, Andreu; Zabalza de Torres, Víctor; 672 coauthors
Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.
http://www.recercat.cat:80/handle/2072/238743First evidence for the annihilation decay mode B+→D+sϕ
http://www.recercat.cat:80/handle/2072/238352
First evidence for the annihilation decay mode B+→D+sϕ
Abellan Beteta, C.; Calvo Gómez, M.; Camboni, Alessandro; Comerma Montells, Albert; Domingo Bonal, F.; Garrido Beltrán, Lluís; Grabalosa Gándara, Marc; Graciani Díaz, Ricardo; Graugés Pous, Eugeni; Lopez Asamar, E.; Pérez-Calero Yzquierdo, Antonio; Picatoste Olloqui, Eduardo; Pie Valls, Blai; Potterat, Cédric; Rives Molina, V.; Ruiz, Hugo (Ruiz Pérez); Vázquez Gómez, R.; Vilasis-Cardona, X.; LHCb Collaboration
Evidence for the hadronic annihilation decay mode B+→D+sϕ is found with greater than 3σ significance. The branching fraction and CP asymmetry are measured to be $ B(B+→D+sϕ)=(1.87+1.25−0.73(stat)±0.19(syst)±0.32(norm))×10−6,ACP(B+→D+sϕ)=−0.01±0.41(stat)±0.03(syst). $ The last uncertainty on B(B+→D+sϕ) is from the branching fractions of the B+→D+sD¯¯¯0 normalization mode and intermediate resonance decays. Upper limits are also set for the branching fractions of the related decay modes B+(c)→D+(s)K∗0,B+(c)→D+(s)K¯¯¯∗0 and B+c→D+sϕ , including the result B(B+→D+K∗0)<1.8×10−6 at the 90% credibility level.
http://www.recercat.cat:80/handle/2072/238352Neutron skin thickness in the droplet model with surface width dependence: Indications of softness of the nuclear symmetry energy
http://www.recercat.cat:80/handle/2072/217255
Neutron skin thickness in the droplet model with surface width dependence: Indications of softness of the nuclear symmetry energy
Warda, M.; Viñas Gausí, Xavier; Roca-Maza, X.; Centelles Aixalà, Mario
We analyze the neutron skin thickness in finite nuclei with the droplet model and effective nuclear interactions. The ratio of the bulk symmetry energy J to the so-called surface stiffness coefficient Q has in the droplet model a prominent role in driving the size of neutron skins. We present a correlation between the density derivative of the nuclear symmetry energy at saturation and the J/Q ratio. We emphasize the role of the surface widths of the neutron and proton density profiles in the calculation of the neutron skin thickness when one uses realistic mean-field effective interactions. Next, taking as experimental baseline the neutron skin sizes measured in 26 antiprotonic atoms along the mass table, we explore constraints arising from neutron skins on the value of the J/Q ratio. The results favor a relatively soft symmetry energy at subsaturation densities. Our predictions are compared with the recent constraints derived from other experimental observables. Though the various extractions predict different ranges of values, one finds a narrow window L∼45-75 MeV for the coefficient L that characterizes the density derivative of the symmetry energy that is compatible with all the different empirical indications.
http://www.recercat.cat:80/handle/2072/217255Percolation of spatially constrained Erdos-R enyi networks with degree correlations
http://www.recercat.cat:80/handle/2072/224825
Percolation of spatially constrained Erdos-R enyi networks with degree correlations
Schmeltzer, C.; Soriano i Fradera, Jordi; Sokolov, Igor M., 1958-; Rüdiger, S.
Motivated by experiments on activity in neuronal cultures [J. Soriano, M. Rodr ́ıguez Mart́ınez, T. Tlusty, and E. Moses, Proc. Natl. Acad. Sci. 105, 13758 (2008)], we investigate the percolation transition and critical exponents of spatially embedded Erd̋os-Ŕenyi networks with degree correlations. In our model networks, nodes are randomly distributed in a two-dimensional spatial domain, and the connection probability depends on Euclidian link length by a power law as well as on the degrees of linked nodes. Generally, spatial constraints lead to higher percolation thresholds in the sense that more links are needed to achieve global connectivity. However, degree correlations favor or do not favor percolation depending on the connectivity rules. We employ two construction methods to introduce degree correlations. In the first one, nodes stay homogeneously distributed and are connected via a distance- and degree-dependent probability. We observe that assortativity in the resulting network leads to a decrease of the percolation threshold. In the second construction methods, nodes are first spatially segregated depending on their degree and afterwards connected with a distance-dependent probability. In this segregated model, we find a threshold increase that accompanies the rising assortativity. Additionally, when the network is constructed in a disassortative way, we observe that this property has little effect on the percolation transition.
http://www.recercat.cat:80/handle/2072/224825Thomas-Fermi theory for atomic nuclei revisited
http://www.recercat.cat:80/handle/2072/217258
Thomas-Fermi theory for atomic nuclei revisited
Centelles Aixalà, Mario; Schuck, Peter; Viñas Gausí, Xavier
The recently developed semiclassical variational Wigner-Kirkwood (VWK) approach is applied to finite nuclei using external potentials and self-consistent mean fields derived from Skyrme inter-actions and from relativistic mean field theory. VWK consist s of the Thomas-Fermi part plus a pure, perturbative h 2 correction. In external potentials, VWK passes through the average of the quantal values of the accumulated level density and total en energy as a function of the Fermi energy. However, there is a problem of overbinding when the energy per particle is displayed as a function of the particle number. The situation is analyzed comparing spherical and deformed harmonic oscillator potentials. In the self-consistent case, we show for Skyrme forces that VWK binding energies are very close to those obtained from extended Thomas-Fermi functionals of h 4 order, pointing to the rapid convergence of the VWK theory. This satisfying result, however, does not cure the overbinding problem, i.e., the semiclassical energies show more binding than they should. This feature is more pronounced in the case of Skyrme forces than with the relativistic mean field approach. However, even in the latter case the shell correction energy for e.g.208 Pb turns out to be only ∼ −6 MeV what is about a factor two or three off the generally accepted value. As an adhoc remedy, increasing the kinetic energy by 2.5%, leads to shell correction energies well acceptable throughout the periodic table. The general importance of the present studies for other finite Fermi systems, self-bound or in external potentials, is pointed out.
http://www.recercat.cat:80/handle/2072/217258Electron scattering in isotonic chains as a probe of the proton shell structure of unstable nuclei
http://www.recercat.cat:80/handle/2072/217217
Electron scattering in isotonic chains as a probe of the proton shell structure of unstable nuclei
Roca-Maza, X.; Centelles Aixalà, Mario; Salvat Gavaldà, Francesc; Viñas Gausí, Xavier
Electron scattering on unstable nuclei is planned in future facilities of the GSI and RIKEN upgrades. Motivated by this fact, we study theoretical predictions for elastic electron scattering in the N=82, N=50, and N=14 isotonic chains from very proton-deficient to very proton-rich isotones. We compute the scattering observables by performing Dirac partial-wave calculations. The charge density of the nucleus is obtained with a covariant nuclear mean-field model that accounts for the low-energy electromagnetic structure of the nucleon. For the discussion of the dependence of scattering observables at low-momentum transfer on the gross properties of the charge density, we fit Helm model distributions to the self-consistent mean-field densities. We find that the changes shown by the electric charge form factor along each isotonic chain are strongly correlated with the underlying proton shell structure of the isotones. We conclude that elastic electron scattering experiments on isotones can provide valuable information about the filling order and occupation of the single-particle levels of protons.
http://www.recercat.cat:80/handle/2072/217217Angular distributions of leptons from J/ ψ's produced in 920 GeV fixed-target proton-nucleus collisions
http://www.recercat.cat:80/handle/2072/238336
Angular distributions of leptons from J/ ψ's produced in 920 GeV fixed-target proton-nucleus collisions
Conde, P.; Garrido Beltrán, Lluís; Peralta, D.; HERA-B Collaboration
A study of the angular distributions of leptons from decays of J/ψ"s produced in p-C and p-W collisions at s√=41.6~GeV has been performed in the J/ψ Feynman-x region −0.34<x F <0.14 and for J/ψ transverse momenta up to 5.4 GeV/c. The data were collected by the HERA-B experiment at the HERA proton ring of the DESY laboratory. The results, based on a clean selection of 2.3×105 J/ψ"s reconstructed in both the e + e − and μ + μ − decay channels, indicate that J/ψ"s are produced polarized. The magnitude of the effect is maximal at low p T . For p T >1 GeV/c a significant dependence on the reference frame is found: the polar anisotropy is more pronounced in the Collins-Soper frame and almost vanishes in the helicity frame, where, instead, a significant azimuthal anisotropy arises.
http://www.recercat.cat:80/handle/2072/238336Dynamic and quasistatic trajectories in quasifission reactions and particle emission
http://www.recercat.cat:80/handle/2072/217306
Dynamic and quasistatic trajectories in quasifission reactions and particle emission
Aleshin, V. P.; Centelles Aixalà, Mario; Viñas Gausí, Xavier; Nicolis, N. G.
We show that the quasifission paths predicted by the one-body dissipation dynamics, in the slowest phase of a binary reaction, follow a quasistatic path, which represents a sequence of states of thermal equilibrium at a fixed value of the deformation coordinate. This establishes the use of the statistical particle-evaporation model in the case of dynamical time-evolving systems. Pre- and post-scission multiplicities of neutrons and total multiplicities of protons and α particles in fission reactions of 63Cu+92Mo, 60Ni+100Mo, 63Cu+100Mo at 10 MeV/u and 20Ne+144,148,154Sm at 20 MeV/u are reproduced reasonably well with statistical model calculations performed along dynamic trajectories whose slow stage (from the most compact configuration up to the point where the neck starts to develop) lasts some 35×10−21 s.
http://www.recercat.cat:80/handle/2072/217306First observation of the decay B+→π+μ+μ−
http://www.recercat.cat:80/handle/2072/238387
First observation of the decay B+→π+μ+μ−
LHCb Collaboration; Abellan Beteta, C.; Calvo Gómez, M.; Camboni, Alessandro; Comerma Montells, Albert; Domingo Bonal, F.; Garrido Beltrán, Lluís; Gascón Fora, David; Grabalosa Gándara, Marc; Graciani Díaz, Ricardo; Graugés Pous, Eugeni; Lopez Asamar, E.; Pérez-Calero Yzquierdo, Antonio; Picatoste Olloqui, Eduardo; Pie Valls, Blai; Potterat, Cédric; Puig Navarro, Albert; Roselló, M.; Ruiz, Hugo (Ruiz Pérez); Vázquez Gómez, R.; Vilasis-Cardona, X.
A discovery of the rare decay B + → π + μ + μ − is presented. This decay is observed for the first time, with 5.2 σ significance. The observation is made using pp collision data, corresponding to an integrated luminosity of 1.0 fb−1, collected with the LHCb detector. The measured branching fraction is (2.3 ± 0.6 (stat.) ± 0.1 (syst.))×10−8, and the ratio of the B + → π + μ + μ − and B + → K + μ + μ − branching fractions is measured to be 0.053 ± 0.014 (stat.) ± 0.001 (syst.).
http://www.recercat.cat:80/handle/2072/238387Quantum chaos in SU(3) models with trapped ions
http://www.recercat.cat:80/handle/2072/222876
Quantum chaos in SU(3) models with trapped ions
Grass, Tobias; Juliá-Díaz, Bruno; Kus, Marek; Lewenstein, M.
A scheme to generate long-range spin-spin interactions between three-level ions in a chain is presented, providing a feasible experimental route to the rich physics of well-known SU(3) models. In particular, we demonstrate different signatures of quantum chaos which can be controlled and observed in experiments with trapped ions.
http://www.recercat.cat:80/handle/2072/222876Versatility of field theory motivated nuclear effective Lagrangian approach
http://www.recercat.cat:80/handle/2072/217282
Versatility of field theory motivated nuclear effective Lagrangian approach
Arumugam, P.; Sharma, B. K.; Sahu, P. K.; Patra, S. K.; Sil, Tapas; Centelles Aixalà, Mario; Viñas Gausí, Xavier
We analyze the results for infinite nuclear and neutron matter using the standard relativistic mean field model and its recent effective field theory motivated generalization. For the first time, we show quantitatively that the inclusion in the effective theory of vector meson self-interactions and scalar-vector cross-interactions explains naturally the recent experimental observations of the softness of the nuclear equation of state, without losing the advantages of the standard relativistic model for finite nuclei.
http://www.recercat.cat:80/handle/2072/217282