Microscopic description of dissipative dynamics of a level crossing transition

We analyze the effect of a dissipative bosonic environment on the Landau-Zener-Stuckelberg-Majorana (LZSM) level crossing model by using a microscopic approach to derive the relevant master equation. For an environment at zero temperature and weak dissipation our microscopic approach confirms the independence of the survival probability on the decay rate that has been predicted earlier by the simple phenomenological LZSM model. For strong decay the microscopic approach predicts a notable increase of the survival probability, which signals dynamical decoupling of the initial state. Unlike the phenomenological model our approach makes it possible to study the dependence of the system dynamics on the temperature of the environment. In the limit of very high temperature we find that the dynamics is characterized by a very strong dynamical decoupling of the initial state - temperature-induced quantum Zeno effect.Comment: 6 pages, 4 figure

Critical behavior of plastic depinning of vortex lattices in two dimensions: Molecular dynamics simulations

Using molecular dynamics simulations, we report a study of the dynamics of two-dimensional vortex lattices driven over a disordered medium. In strong disorder, when topological order is lost, we show that the depinning transition is analogous to a second order critical transition: the velocity-force response at the onset of motion is continuous and characterized by critical exponents. Combining studies at zero and nonzero temperature and using a scaling analysis, two critical expo- nents are evaluated. We find v\sim (F-F_c)^\beta with \beta=1.3\pm0.1 at T=0 and F>F_c, and v\sim T^{1/\delta} with \delta^{-1}=0.75\pm0.1 at F=F_c, where F_c is the critical driving force at which the lattice goes from a pinned state to a sliding one. Both critical exponents and the scaling function are found to exhibit universality with regard to the pinning strength and different disorder realizations. Furthermore, the dynamics is shown to be chaotic in the whole critical region.Comment: 8 pages, 6 figure

The elastic depinning transition of vortex lattices in two dimensions

Large scale numerical simulations are used to study the elastic dynamics of two-dimensional vortex lattices driven on a disordered medium in the case of weak disorder. We investigate the so-called elastic depinning transition by decreasing the driving force from the elastic dynamical regime to the state pinned by the quenched disorder. Similarly to the plastic depinning transition, we find results compatible with a second order phase transition, although both depinning transitions are very different from many viewpoints. We evaluate three critical exponents of the elastic depinning transition. $\beta = 0.29 \pm 0.03$ is found for the velocity exponent at zero temperature, and from the velocity-temperature curves we extract the critical exponent $\delta^{-1} = 0.28 \pm 0.05$. Furthermore, in contrast with charge-density waves, a finite-size scaling analysis suggests the existence of a unique diverging length at the depinning threshold with an exponent $\nu= 1.04 \pm 0.04$, which controls the critical force distribution, the finite-size crossover force distribution and the intrinsic correlation length. Finally, a scaling relation is found between velocity and temperature with the $\beta$ and $\delta$ critical exponents both independent with regard to pinning strength and disorder realizations.Comment: 17 pages, 10 figure

Stimulated Raman adiabatic passage in an open quantum system: Master equation approach

A master equation approach to the study of environmental effects in the adiabatic population transfer in three-state systems is presented. A systematic comparison with the non-Hermitian Hamiltonian approach [N. V. Vitanov and S. Stenholm, Phys. Rev. A {\bf 56}, 1463 (1997)] shows that in the weak coupling limit the two treatments lead to essentially the same results. Instead, in the strong damping limit the predictions are quite different: in particular the counterintuitive sequences in the STIRAP scheme turn out to be much more efficient than expected before. This point is explained in terms of quantum Zeno dynamics.Comment: 11 pages, 4 figure

Zeno-like phenomena in STIRAP processes

The presence of a continuous measurement quantum Zeno effect in a Stimulated Rapid Adiabatic Passage is studied, exploring in detail a sort of self-competition of the damping, which drives the system toward a loss of population and, at the same time, realizes the conditions to optimize the adiabatic passag

Classes of behavior of small-world networks

Small-world networks are the focus of recent interest because they appear to circumvent many of the limitations of either random networks or regular lattices as frameworks for the study of interaction networks of complex systems. Here, we report an empirical study of the statistical properties of a variety of diverse real-world networks. We present evidence of the occurrence of three classes of small-world networks: (a) scale-free networks, characterized by a vertex connectivity distribution that decays as a power law; (b) broad-scale networks, characterized by a connectivity distribution that has a power-law regime followed by a sharp cut-off; (c) single-scale networks, characterized by a connectivity distribution with a fast decaying tail. Moreover, we note for the classes of broad-scale and single-scale networks that there are constraints limiting the addition of new links. Our results suggest that the nature of such constraints may be the controlling factor for the emergence of different classes of networks

Dynamic identification of a strategic building of the sixties with a mixed structure

The present paper shows and discusses the results of the identification procedure applied to the building of the Municipality of Castellaneta, Taranto (Puglia, Italy). The case study has been chosen for its structural complexity; indeed, the building has been built in two successive phases, block A built between 1955 and 1957, and block B, for completion, presumably built between the years 1960 and 1961. Block A constitutes the main building and represents the original nucleus. The structure was subsequently subject to structural interventions to replace some load-bearing walls with steel beams. The building constituting block B, joined to the original body of the building, has a structure in load-bearing masonry, while the floors, more recently built, are also in brick-concrete, but with pre-cast prestressed joists. The dynamic response of the building was assessed through OMA (Operational Modal Analysis) identification technique which allows you to determine the properties of the structure in real operating conditions, without the need to interrupt the activities inside the structure itself. The structural excitement, therefore, is due only to the environmental condition. A 3D model was defined in PRO_SAP; the results obtained from the finite element model were subsequently compared with those obtained from the experimental model

High rate continuous biohydrogen production by hyperthermophilic Thermotoga neapolitana

This study focused on continuous-flow hydrogen production by Thermotoga neapolitana at a hydraulic retention time (HRT) decreasing from 24 to 5 h. At each HRT reduction, the hydrogen yield (HY) immediately dropped, but recovered during prolonged cultivation at constant HRT. The final HY in each operating period decreased from 3.4 (±0.1) to 2.0 (±0.0) mol H2/mol glucose when reducing the HRT from 24 to 7 h. Simultaneously, the hydrogen production rate (HPR) and the liquid phase hydrogen concentration (H2aq) increased from 82 (±1) to 192 (±4) mL/L/h and from 9.1 (±0.3) to 15.6 (±0.7) mL/L, respectively. Additionally, the effluent glucose concentration increased from 2.1 (±0.1) to above 10 mM. Recirculating H2-rich biogas prevented the supersaturation of H2aq reaching a value of 9.3 (±0.7) mL/L, resulting in complete glucose consumption and the highest HPR of 277 mL/L/h at an HRT of 5 h