The European Physical Journal B

We investigate the role of the colored noise in two biological systems: (i) adults of Nezara viridula (L.) (Heteroptera: Pentatomidae), and (ii) polymer translocation. In the first system we analyze, by directionality tests, the response of N. viridula individuals to subthreshold signals plus noise in their mating behaviour. The percentage of insects that react to the subthreshold signal shows a nonmonotonic behaviour, characterized by the presence of a maximum, as a function of the noise intensity. This is the signature of the non-dynamical stochastic resonance phenomenon. By using a “soft” threshold model we find that the maximum of the input-output cross correlation occurs in the same range of noise intensity values for which the behavioural activation of the insects has a maximum. Moreover this maximum value is lowered and shifted towards higher noise intensities, compared to the case of white noise. In the second biological system the noise driven translocation of short polymers in crowded solutions is analyzed. An improved version of the Rouse model for a flexible polymer is adopted to mimic the molecular dynamics by taking into account both the interactions between adjacent monomers and the effects of a Lennard-Jones potential between all beads. The polymer dynamics is simulated in a two-dimensional domain by numerically solving the Langevin equations of motion in the presence of thermal fluctuations and a colored noise source. At low temperatures or for strong colored noise intensities the translocation process of the polymer chain is delayed. At low noise intensity, as the polymer length increases, we find a nonmonotonic behaviour for the mean first translocation time of the polymer centre of inertia. We show how colored noise influences the motion of short polymers, by inducing two different regimes of translocation in the dynamics of molecule transport.

There has been a debate in the transportation research community over the validity of a class of traffic flow models. These models have the peculiar property that one of its characteristic speeds is faster than that of vehicular traffic. This note attempts to provide an overview of the diverging views on how to interpret this property, and specific comments on the interpretation of Helbing and Johansson [On the controversy around Daganzo’s requiem for and Aw-Rascle’s resurrection of second-order traffic flow models, Eur. Phys. J. B (2009), DOI: 10.1140/epjb/e2009-00182-7]. We showed that having faster-than-traffic characteristics does produce counterintuitive predictions, and they cannot be explained away by a linear stability analysis. As such, the existence of such characteristics must be justified by the physics of traffic, and verified through empirical observations.

I consider a theoretical description of recent experiments on doping the spin-Peierls compound CuGeO3 and the Haldane gap compounds PbNi2V2O8 and Y2BaNiO5. The effective theory is the one of randomly distributed spin-1/2 moments interacting with an exchange decaying exponentially with distance. The model has two phases in the (doping, interchain coupling) plane: (i) a Néel ordered phase at small doping; (ii) a quantum disordered phase at larger doping and small interchain interactions. The spin-Peierls compound CuGeO3 and the Haldane gap nickel oxides PbNi2V2O8 and Y2BaNiO5 fit well into this phase diagram. At small temperature, the Néel phase is found to be reentrant into the quantum disordered region. The Néel transition relevant for CuGeO3 and PbNi2V2O8 can be described in terms of a classical disordered model. A simplified version of this model is introduced, and is solved on a hierarchical lattice structure, which allows to discuss the renormalization group flow of the model. It is found that the system looks non disordered at large scale, which is not against available susceptibility experiments. In the quantum disordered regime relevant for Y2BaNiO5, the two spin model and the cluster RG in the 1D regime show a power law susceptibility, in agreement with recent experiments on Y2BaNiO5. It is found that there is a succession of two distinct quantum disordered phases as the temperature is decreased. The classical disordered model of the doped spin-1chain contains already a physics relevant to the quantum disordered phase.

We investigate the dynamics of matter-wave solitons in the one-dimensional (1-D) Gross-Pitaevskii (GP) equation describing Bose-Einstein condensates (BECs) with time-dependent scattering length in varying trapping potentials with feeding/loss term. By performing a modified lens-type transformation, we reduce the GP equation into a classical nonlinear Schrödinger (NLS) equation with distributed coefficients and find its integrable condition. Under the integrable condition, we apply the generalized Jacobian elliptic function method (GJEFM) and present exact analytical solutions which describe the propagation of a bright and dark solitons in BECs. Their stability is examined using analytic method. The obtained exact solutions show that the amplitude of bright and dark solitons depends on the scattering length, while their motion and the total number of BEC atoms depend on the external trapping potential. Our results also shown that the loss of atoms can dominate the aggregation of atoms by the attractive interaction, and thus the peak density can decrease in time despite that the strength of the attractive interaction is increased.

We have used neutron reflectometry to measure interfacial widths between two polystyrene films, where either one or both films are crosslinked. The observed interfacial width between two networks is larger than the size expected for “dangling ends”, which suggests motion of heterogeneous regions of the networks. In the case when one of the networks is replaced by a linear polymer, the interfacial profile can be asymmetric with a diffusion “front” of linear polymer penetrating the network to a length scale of up to 200 Å. In the case of a more densely crosslinked network and a high molecular weight linear polymer the interface is symmetric implying negligible penetration.

We present a novel model to simulate real social networks of complex interactions, based in a system of colliding particles (agents). The network is build by keeping track of the collisions and evolves in time with correlations which emerge due to the mobility of the agents. Therefore, statistical features are a consequence only of local collisions among its individual agents. Agent dynamics is realized by an event-driven algorithm of collisions where energy is gained as opposed to physical systems which have dissipation. The model reproduces empirical data from networks of sexual interactions, not previously obtained with other approaches.

Transient solutions of the inhomogeneous Maxwell equations are obtained. The specific current source belongs to the spherical surface expanding with the velocity of light. Representations of the electromagnetic field components in the spherical coordinates in terms of the Fourier series are found. The obtained solutions are correct near the wavefront. The general expressions are applied to a description of electromagnetic waves produced by different sources and to a discussion of formation of directional waves and the family of relatively undistorted waves.

The localization properties of eigenfunctions for two interacting particles in the one-dimensional Anderson model are studied for system sizes up to N = 5000 sites corresponding to a Hilbert space of dimension ≈107 using the Green function Arnoldi method. The eigenfunction structure is illustrated in position, momentum and energy representation, the latter corresponding to an expansion in non-interacting product eigenfunctions. Different types of localization lengths are computed for parameter ranges in system size, disorder and interaction strengths inaccessible until now. We confirm that one-parameter scaling theory can be successfully applied provided that the condition of N being significantly larger than the one-particle localization length L 1 is verified. The enhancement effect of the two-particle localization length L 2 behaving as L 2 ~ L 2 1 is clearly confirmed for a certain quite large interval of optimal interactions strengths. Further new results for the interaction dependence in a very large interval, an energy value outside the band center, and different interaction ranges are obtained.

Nghiên cứu các hợp chất dựa trên Fe đã thu hút nhiều sự chú ý do phát hiện ra tính siêu dẫn cũng như nhiều đặc tính điện tử kỳ lạ khác. Trong bài viết này, chúng tôi sẽ tổng hợp một số công trình nghiên cứu của chúng tôi trên những vật liệu này được thực hiện bằng phương pháp lý thuyết chức năng mật độ và quang phổ phát xạ điện tử góc. Các kết quả được trình bày tại đây chỉ ra rằng tính chiều không gian của cấu trúc điện tử cơ bản đóng vai trò quan trọng trong việc dẫn đến các thuộc tính điện tử thú vị của chúng. Tính nematic được tìm thấy trong hầu hết các vật liệu này dường như có liên quan đến trật tự từ xa dài. Chúng tôi lập luận rằng tính kỳ lạ trong các thuộc tính điện tử có liên quan đến sự tinh tế trong những bất ổn định cấu trúc và từ tính mà các vật liệu này đang có.