Coherent quantum transport in disordered systems I: The influence of dephasing on the transport properties and absorption spectra on one-dimensional systems

Excitonic transport in static disordered one dimensional systems is studied in the presence of thermal fluctuations that are described by the Haken-Strobl-Reineker model. For short times, non-diffusive behavior is observed that can be characterized as the free-particle dynamics in the Anderson localized system. Over longer time scales, the environment-induced dephasing is sufficient to overcome the Anderson localization caused by the disorder and allow for transport to occur which is always seen to be diffusive. In the limiting regimes of weak and strong dephasing quantum master equations are developed, and their respective scaling relations imply the existence of a maximum in the diffusion constant as a function of the dephasing rate that is confirmed numerically. In the weak dephasing regime, it is demonstrated that the diffusion constant is proportional to the square of the localization length which leads to a significant enhancement of the transport rate over the classical prediction. Finally, the influence of noise and disorder on the absorption spectrum is presented and its relationship to the transport properties is discussed.Comment: 23 pages, 7 figure

Application of quantum coherence and decoherence

Coherent phenomena in molecular chromophores interacting with a dissipative environment is addressed. We defined coherence by the phenomena of decoherence which collapses the system to pointer states. Coherent irreducible phenomena takes place in a time window before the system collapses. We describe a computational model: The Stochastic Surrogate Hamiltonian that can deal with such complex quantum systems. The conditions for coherent control are analyzed. A prerequisite for coherent phenomena is the ability to perform coherent control using shaped light sources. We show that weak field coherent control is enabled by interaction with the environment.Israel Science Foundatio

Dublin City University at CLEF 2004: experiments in monolingual, bilingual and multilingual retrieval

The Dublin City University group participated in the monolingual, bilingual and multilingual retrieval tasks this year. The main focus of our investigation this year was extending our retrieval system to document languages other than English, and completing the multilingual task comprising four languages: English, French, Russian and Finnish. Results from our French monolingual experiments indicate that working in French is more effective for retrieval than adopting document and topic translation to English. However, comparison of our multilingual retrieval results using different topic and document translation reveals that this result does not extend to retrieved list merging for the multilingual task in a simple predictable way

On the temperature dependence of the interaction-induced entanglement

Both direct and indirect weak nonresonant interactions are shown to produce entanglement between two initially disentangled systems prepared as a tensor product of thermal states, provided the initial temperature is sufficiently low. Entanglement is determined by the Peres-Horodeckii criterion, which establishes that a composite state is entangled if its partial transpose is not positive. If the initial temperature of the thermal states is higher than an upper critical value $T_{uc}$ the minimal eigenvalue of the partially transposed density matrix of the composite state remains positive in the course of the evolution. If the initial temperature of the thermal states is lower than a lower critical value $T_{lc}\leq T_{uc}$ the minimal eigenvalue of the partially transposed density matrix of the composite state becomes negative which means that entanglement develops. We calculate the lower bound $T_{lb}$ for $T_{lc}$ and show that the negativity of the composite state is negligibly small in the interval $T_{lb}<T<T_{uc}$. Therefore the lower bound temperature $T_{lb}$ can be considered as \textit{the} critical temperature for the generation of entanglement.Comment: 27 pages and 7 figure

Two-Phase Flow Modeling of Cryogenic Loading Operations

We consider problem of modeling and controlling two-phase cryogenic flows during ground loading operations. We introduce homogeneous moving front and separated two-phase flow solvers that are capable of fast and accurate online predictions of flow dynamics during chilldown and transfer under nominal conditions and in the presence of faults. Concise sets of cryogenic correlations are proposed in each case. We present results of application of proposed solvers to the analysis of chilldown in large-scale experimental cryogenic transfer line build in Kennedy Space Center. We discuss optimization of parameters of cryogenic models obtained using general inferential framework and an application of the solvers to the fault detection and evaluation based on D-matrix approach. It is shown that solver’s predictions are in good agreement with experimental data obtained for liquid nitrogen flow in nominal regime and in the presence of faults

Risk Assessment and scaling for the SLS LOx ET

In this report we analyze the transpiration cooling by He bubble injection of the long LOx tank feedline heated by the environment heat. We consider possible hazards that can arise in the proposed design of the SLS core stage where the feedline length is much longer than that used in the Space Shuttle

Minimizing the population extinction risk by migration

Many populations in nature are fragmented: they consist of local populations occupying separate patches. A local population is prone to extinction due to the shot noise of birth and death processes. A migrating population from another patch can dramatically delay the extinction. What is the optimal migration rate that minimizes the extinction risk of the whole population? Here we answer this question for a connected network of model habitat patches with different carrying capacities.Comment: 7 pages, 3 figures, accepted for publication in PRL, appendix contains supplementary materia

Fast migration and emergent population dynamics

We consider population dynamics on a network of patches, each of which has a the same local dynamics, with different population scales (carrying capacities). It is reasonable to assume that if the patches are coupled by very fast migration the whole system will look like an individual patch with a large effective carrying capacity. This is called a "well-mixed" system. We show that, in general, it is not true that the well-mixed system has the same dynamics as each local patch. Different global dynamics can emerge from coupling, and usually must be figured out for each individual case. We give a general condition which must be satisfied for well-mixed systems to have the same dynamics as the constituent patches.Comment: 4 page

Risk Assessment and Scaling for the SLS LH2 ET

In this report the main physics processes in LH2 tank during prepress and rocket flight are studied. The goal of this investigation is to analyze possible hazards and to make risk assessment in proposed LH2 tank designs for SLS with 5 engines (the situation with 4 engines is less critical). For analysis we use the multinode model (MNM) developed by us and presented in a separate report and also 3D ANSYS simulations. We carry out simulation and theoretical analysis the physics processes such as (i) accumulation of bubbles in LH2 during replenish stage and their collapsing in the liquid during the prepress; (ii) condensation-evaporation at the liquid-vapor interface and tank wall, (iv) heating the liquid near the interface and wall due to condensation and environment heat, (v) injection of hot He during prepress and of hot GH2 during flight, (vi) mixing and cooling of the injected gases due to heat transfer between the gases, liquid and the tank wall. We analyze the effects of these physical processes on the thermo- and fluid gas dynamics in the ullage and on the stratification of temperature in the liquid and assess the associated hazards. A special emphasize is put on the scaling predictions for the larger SLS LH2 tank

The rise and fall of quantum and classical correlations in open-system dynamics

Interacting quantum systems evolving from an uncorrelated composite initial state generically develop quantum correlations -- entanglement. As a consequence, a local description of interacting quantum system is impossible as a rule. A unitarily evolving (isolated) quantum system generically develops extensive entanglement: the magnitude of the generated entanglement will increase without bounds with the effective Hilbert space dimension of the system. It is conceivable, that coupling of the interacting subsystems to local dephasing environments will restrict the generation of entanglement to such extent, that the evolving composite system may be considered as approximately disentangled. This conjecture is addressed in the context of some common models of a bipartite system with linear and nonlinear interactions and local coupling to dephasing environments. Analytical and numerical results obtained imply that the conjecture is generally false. Open dynamics of the quantum correlations is compared to the corresponding evolution of the classical correlations and a qualitative difference is found.Comment: 35 pages, 10 figures. Revised according to comments of the referees. Accepted for publication in Phys. Rev.