RECERCAT - Articles publicats en revistes (Estructura i Constituents de la Matèria)
http://www.recercat.cat:80/handle/2072/48808
www.ub.eduMon, 21 Apr 2014 02:31:36 GMT2014-04-21T02:31:36ZThe Channel Imagehttp://www.recercat.cat:80/bitstream/id/26376/
http://www.recercat.cat:80/handle/2072/48808
Identification of neuronal network properties from the spectral analysis of calcium imaging signals in neuronal cultures
http://www.recercat.cat:80/handle/2072/228080
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/2072/228080Topological phases in small quantum Hall samples
http://www.recercat.cat:80/handle/2072/227666
Topological phases in small quantum Hall samples
Grass, Tobias; Juliá-Díaz, Bruno; Lewenstein, M.
Topological order has proven a useful concept to describe quantum phase transitions which are not captured by the Ginzburg-Landau type of symmetry-breaking order. However, lacking a local order parameter, topological order is hard to detect. One way to detect it is via direct observation of anyonic properties of excitations which are usually discussed in the thermodynamic limit, but so far has not been realized in macroscopic quantum Hall samples. Here we consider a system of few interacting bosons subjected to the lowest Landau level by a gauge potential, and theoretically investigate vortex excitations in order to identify topological properties of different ground states. Our investigation demonstrates that even in surprisingly small systems anyonic properties are able to characterize the topological order. In addition, focusing on a system in the Laughlin state, we study the robustness of its anyonic behavior in the presence of tunable finite-range interactions acting as a perturbation. A clear signal of a transition to a different state is reflected by the system's anyonic properties.
http://www.recercat.cat:80/handle/2072/227666Asymmetric stochastic switching driven by intrinsic molecular noise
http://www.recercat.cat:80/handle/2072/227173
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/2072/227173Asymmetric 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/2072/227133Langevin 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<br>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<br>Hiliard<br>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/2072/226985Percolation 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/2072/224825Quantum Hall Phases of two-component bosons
http://www.recercat.cat:80/handle/2072/224824
Quantum Hall Phases of two-component bosons
Grass, Tobias; Raventós, D.; Lewenstein, M.; Juliá-Díaz, Bruno
The recent production of synthetic magnetic fields acting on electroneutral particles, such as atoms or photons, has boosted interest in the quantum Hall physics of bosons. Adding pseudospin 1/2 to the bosons greatly enriches the scenario, as it allows them to form an interacting integer quantum Hall (IQH) phase with no fermionic counterpart. Here we show that, for a small two-component Bose gas on a disk, the complete strongly correlated regime, extending from the integer phase at filling factor ν = 2 to the Halperin phase at filling factor ν = 2 / 3, is well described by composite fermionization of the bosons. Moreover we study the edge excitations of the IQH state, which, in agreement with expectations from topological field theory, are found to consist of forward-moving charge excitations and backward-moving spin excitations. Finally, we demonstrate how pair-correlation functions allow one to experimentally distinguish the IQH state from competing states, such as non-Abelian spin singlet (NASS) states.
http://www.recercat.cat:80/handle/2072/224824Matching stages of heavy-ion collision models
http://www.recercat.cat:80/handle/2072/224722
Matching stages of heavy-ion collision models
Cheng, Yun; Csernai, L. P.; Magas, V. K.; Schlei, B. R.; Strottman, D.
Heavy-ion reactions and other collective dynamical processes are frequently described by different theoretical approaches for the different stages of the process, like initial equilibration stage, intermediate locally equilibrated fluid dynamical stage, and final freeze-out stage. For the last stage, the best known is the Cooper-Frye description used to generate the phase space distribution of emitted, noninteracting particles from a fluid dynamical expansion or explosion, assuming a final ideal gas distribution, or (less frequently) an out-of-equilibrium distribution. In this work we do not want to replace the Cooper-Frye description, but rather clarify the ways of using it and how to choose the parameters of the distribution and, eventually, how to choose the form of the phase space distribution used in the Cooper-Frye formula. Moreover, the Cooper-Frye formula is used in connection with the freeze-out problem, while the discussion of transition between different stages of the collision is applicable to other transitions also. More recently, hadronization and molecular dynamics models have been matched to the end of a fluid dynamical stage to describe hadronization and freeze-out. The stages of the model description can be matched to each other on space-time hypersurfaces (just like through the frequently used freeze-out hypersurface). This work presents a generalized description of how to match the stages of the description of a reaction to each other, extending the methodology used at freeze-out, in simple covariant form which is easily applicable in its simplest version for most applications.
http://www.recercat.cat:80/handle/2072/224722Local description of quantum inseparability
http://www.recercat.cat:80/handle/2072/224721
Local description of quantum inseparability
Sanpera Trigueros, Anna; Tarrach, R., 1948-; Vidal Bonafont, Guifré
We show how to decompose any density matrix of the simplest binary composite systems, whether separable or not, in terms of only product vectors. We determine for all cases the minimal number of product vectors needed for such a decomposition. Separable states correspond to mixing from one to four pure product states. Inseparable states can be described as pseudomixtures of four or five pure product states, and can be made separable by mixing them with one or two pure product states.
http://www.recercat.cat:80/handle/2072/224721On the interplay between Q^2 and t dependence in exclusive diffractive production of real photons and vector mesons in ep collisions
http://www.recercat.cat:80/handle/2072/224463
On the interplay between Q^2 and t dependence in exclusive diffractive production of real photons and vector mesons in ep collisions
Fiore, Roberto; Jenkovszky, Lázsló L.; Lavorini, A.; Magas, V. K.
We show how the familiar phenomenological way of combining the Q2 (photon virtuality) and t (squared momentum transfer) dependences of the scattering amplitude in Deeply Virtual Compton Scattering (DVCS) [1, 2] and Vector Meson Production (VMP) [2] processes can be understood in an off-mass-shell generalization of dual amplitudes with Mandelstam analyticity [3]. By comparing different approaches, we managed also to constrain the numerical values of the free parameters.
http://www.recercat.cat:80/handle/2072/224463Low-mass diffraction dissociation at the LHC ; role of the background
http://www.recercat.cat:80/handle/2072/224462
Low-mass diffraction dissociation at the LHC ; role of the background
Jenkovszky, Lázsló L.; Kuprash, O. E.; Magas, V. K.
A dual model with a nonlinear proton Regge trajectory in the missing mass (M_X^2) channel is constructed. A background based on a direct-channel exotic trajectory, developed and applied earlier for the inclusive electron-proton cross section description in the nucleon resonance region, is used. The parameters of the model are determined from the extrapolations to earlier experiments. Predictions for the low-mass (2 < M_X^2 < 8GeV^2) diffraction dissociation cross sections at the LHC energies are given.
http://www.recercat.cat:80/handle/2072/224462Momentum 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/2072/224409Fluid dynamical prediction of changed v1-flow at energies available at the CERN Large Hadron Collider
http://www.recercat.cat:80/handle/2072/224408
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/2072/224408Quantum 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/2072/222876Giant 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/2072/220110Electric dipole polarizability in 208Pb: insights from the droplet model
http://www.recercat.cat:80/handle/2072/220109
Electric dipole polarizability in 208Pb: insights from the droplet model
Roca-Maza, X.; Brenna, M.; Colò, G.; Centelles Aixalà, Mario; Viñas Gausí, Xavier; Agrawal, B. K.; Paar, N.; Vretenar, D.; Piekarewicz, J.
We study the electric dipole polarizability α D in 208 Pb based on the predictions of a large and representative set of relativistic and nonrelativistic nuclear mean-field models. We adopt the droplet model as a guide to better understand the correlations between α D and other isovector observables. Insights from the droplet model suggest that the product of α D and the nuclear symmetry energy at saturation density J is much better correlated with the neutron skin thickness r np of 208 Pb than the polarizability alone. Correlations of α D J with r np and with the symmetry energy slope parameter L suggest that α D J is a strong isovector indicator. Hence, we explore the possibility of constraining the isovector sector of the nuclear energy density functional by comparing our theoretical predictions against measurements of both α D and the parity-violating asymmetry in 208 Pb. We find that the recent experimental determination of α D in 208 Pb in combination with the range for the symmetry energy at saturation density J = [31 ± (2) est] MeV suggests r np (208 Pb) = 0 . 165 ± (0 . 009) expt ± (0 . 013) theor ± (0.021) est fm and L = 43 ± (6) expt ± (8) theor ± (12) est MeV
http://www.recercat.cat:80/handle/2072/220109Model-Free Reconstruction of Excitatory Neuronal Connectivity from Calcium Imaging Signals
http://www.recercat.cat:80/handle/2072/218394
Model-Free Reconstruction of Excitatory Neuronal Connectivity from Calcium Imaging Signals
Stetter, Olav; Battaglia, Demian; Soriano i Fradera, Jordi; Geisel, Theo
A systematic assessment of global neural network connectivity through direct electrophysiological assays has remained technically infeasible, even in simpler systems like dissociated neuronal cultures. We introduce an improved algorithmic approach based on Transfer Entropy to reconstruct structural connectivity from network activity monitored through calcium imaging. We focus in this study on the inference of excitatory synaptic links. Based on information theory, our method requires no prior assumptions on the statistics of neuronal firing and neuronal connections. The performance of our algorithm is benchmarked on surrogate time series of calcium fluorescence generated by the simulated dynamics of a network with known ground-truth topology. We find that the functional network topology revealed by Transfer Entropy depends qualitatively on the time-dependent dynamic state of the network (bursting or non-bursting). Thus by conditioning with respect to the global mean activity, we improve the performance of our method. This allows us to focus the analysis to specific dynamical regimes of the network in which the inferred functional connectivity is shaped by monosynaptic excitatory connections, rather than by collective synchrony. Our method can discriminate between actual causal influences between neurons and spurious non-causal correlations due to light scattering artifacts, which inherently affect the quality of fluorescence imaging. Compared to other reconstruction strategies such as cross-correlation or Granger Causality methods, our method based on improved Transfer Entropy is remarkably more accurate. In particular, it provides a good estimation of the excitatory network clustering coefficient, allowing for discrimination between weakly and strongly clustered topologies. Finally, we demonstrate the applicability of our method to analyses of real recordings of in vitro disinhibited cortical cultures where we suggest that excitatory connections are characterized by an elevated level of clustering compared to a random graph (although not extreme) and can be markedly non-local.
http://www.recercat.cat:80/handle/2072/218394Critical Behavior and Axis Defining Symmetry Breaking in Hydra Embryonic Development
http://www.recercat.cat:80/handle/2072/218393
Critical Behavior and Axis Defining Symmetry Breaking in Hydra Embryonic Development
Gamba, Andrea; Nicodemi, Mario; Soriano i Fradera, Jordi; Ott, Albrecht
The formation of a hollow cellular sphere is often one of the first steps of multicellular embryonic development. In the case of Hydra, the sphere breaks its initial symmetry to form a foot-head axis. During this process a gene, ks1, is increasingly expressed in localized cell domains whose size distribution becomes scale-free at the axis-locking moment. We show that a physical model based solely on the production and exchange of ks1-promoting factors among neighboring cells robustly reproduces the scaling behavior as well as the experimentally observed spontaneous and temperature-directed symmetry breaking.
http://www.recercat.cat:80/handle/2072/218393Neutron skin of 208Pb, nuclear symmetry energy, and the parity radius experiment
http://www.recercat.cat:80/handle/2072/217610
Neutron skin of 208Pb, nuclear symmetry energy, and the parity radius experiment
Roca-Maza, X.; Centelles Aixalà, Mario; Viñas Gausí, Xavier; Warda, M.
A precise determination of the neutron skin thickness of a heavy nucleus sets a basic constraint on the nuclear symmetry energy (the neutron skin thickness is the difference of the neutron and proton rms radii of the nucleus). The parity radius experiment (PREX) may achieve it by electroweak parity-violating electron scattering (PVES) on 208Pb. We investigate PVES in nuclear mean field approach to allow the accurate extraction of the neutron skin thickness of 208Pb from the parity-violating asymmetry probed in the experiment. We demonstrate a high linear correlation between the parity-violating asymmetry and the neutron skin thickness in successful mean field forces as the best means to constrain the neutron skin of 208Pb from PREX, without assumptions on the neutron density shape. Continuation of the experiment with higher precision in the parity-violating asymmetry is motivated since the present method can support it to constrain the density slope of the nuclear symmetry energy to new accuracy.
http://www.recercat.cat:80/handle/2072/217610Dynamic 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/2072/217306Nuclear 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/2072/217307Scaling in relativistic Thomas-Fermi approach for nuclei
http://www.recercat.cat:80/handle/2072/217305
Scaling in relativistic Thomas-Fermi approach for nuclei
Patra, S. K.; Centelles Aixalà, Mario; Viñas Gausí, Xavier; Estal, Manuel del
By using the scaling method we derive the virial theorem for the relativistic mean field model of nuclei treated in the Thomas<br>Fermi approach. The Thomas<br>Fermi solutions statisfy the stability condition against scaling. We apply the formalism to study the excitation energy of the breathing mode in finite nuclei with several relativistic parameter sets of common use.
http://www.recercat.cat:80/handle/2072/217305Scaling calculation of isoscalar giant resonances in relativistic Thomas-Fermi theory
http://www.recercat.cat:80/handle/2072/217283
Scaling calculation of isoscalar giant resonances in relativistic Thomas-Fermi theory
Patra, S. K.; Viñas Gausí, Xavier; Centelles Aixalà, Mario; Estal, Manuel del
We derive analytical expressions for the excitation energy of the isoscalar giant monopole and quadrupole resonances in finite nuclei, by using the scaling method and the extended Thomas<br>Fermi approach to relativistic mean-field theory. We study the ability of several nonlinear σ<br>ω parameter sets of common use in reproducing the experimental data. For monopole oscillations the calculations agree better with experiment when the nuclear matter incompressibility of the relativistic interaction lies in the range 220<br>260 MeV. The breathing-mode energies of the scaling method compare satisfactorily with those obtained in relativistic RPA and time-dependent mean-field calculations. For quadrupole oscillations, all the analyzed nonlinear parameter sets reproduce the empirical trends reasonably well.
http://www.recercat.cat:80/handle/2072/217283Versatility 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/2072/217282Bose-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/2072/217281Nuclear 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/2072/217280Nuclear 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/2072/217257Incompressibility 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/2072/217256Thomas-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/2072/217258Microscopic-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/2072/217253