Exact Stochastic Unraveling of an Optical Coherence Dynamics by Cumulant Expansion

A numerically exact Monte Carlo scheme for calculation of open quantum system dynamics is proposed and implemented. The method consists of a Monte-Carlo summation of a perturbation expansion in terms of trajectories in Liouville phase-space with respect to the coupling between the excited states of the molecule. The trajectories are weighted by a complex decoherence factor based on the second-order cumulant expansion of the environmental evolution. The method can be used with an arbitrary environment characterized by a general correlation function and arbitrary coupling strength. It is formally exact for harmonic environments, and it can be used with arbitrary temperature. Time evolution of an optically excited Frenkel exciton dimer representing a molecular exciton interacting with a charge transfer state is calculated by the proposed method. We calculate the evolution of the optical coherence elements of the density matrix and linear absorption spectrum, and compare them with the predictions of standard simulation methods.Comment: 11 pages, 6 figure

Why would plant species become extinct locally if growing conditions improve?

wo assumptions underlie current models of the geographical ranges of perennial plant species: 1. current ranges are in equilibrium with the prevailing climate, and 2. changes are attributable to changes in macroclimatic factors, including tolerance of winter cold, the duration of the growing season, and water stress during the growing season, rather than to biotic interactions. These assumptions allow model parameters to be estimated from current species ranges. Deterioration of growing conditions due to climate change, e.g. more severe drought, will cause local extinction. However, for many plant species, the predicted climate change of higher minimum temperatures and longer growing seasons means, improved growing conditions. Biogeographical models may under some circumstances predict that a species will become locally extinct, despite improved growing conditions, because they are based on an assumption of equilibrium and this forces the species range to match the species-specific macroclimatic thresholds. We argue that such model predictions should be rejected unless there is evidence either that competition influences the position of the range margins or that a certain physiological mechanism associated with the apparent improvement in growing conditions negatively affects the species performance. We illustrate how a process-based vegetation model can be used to ascertain whether such a physiological cause exists. To avoid potential modelling errors of this type, we propose a method that constrains the scenario predictions of the envelope models by changing the geographical distribution of the dominant plant functional type. Consistent modelling results are very important for evaluating how changes in species areas affect local functional trait diversity and hence ecosystem functioning and resilience, and for inferring the implications for conservation management in the face of climate change

European Information System for Organic Markets (EISFOM QLK5-2002-02400): WP 2: “Data collection and processing systems (DCPS) for the conventional markets” and WP 3: “Data collection and processing systems for organic markets” = Deliverable D2

European markets for organic products are developing fast. In Europe, as other parts of the world, more and more farm land is being converted to organic production. In order to adjust production and consumption levels, detailed market information is needed, especially where decisions with a long-term impact need to be taken, for example on converting specific land or livestock enterprises requiring high levels of investment in glasshouses, housing, processing facilities etc. Since public subsidies (regional / national / European) are heavily involved in these investments, valid, accurate and up-to-date information is essential not only for farmers and growers, but also for policy-makers, consultants, processing industry etc. EU-research projects such as OFCAP (FAIR3-CT96-1794) and OMIaRD (QLK5-2000-01124) have shown that regional or national data gathering takes place in many countries, but often only very basic data are reported, such as certified organic holdings, land areas and livestock numbers. Important market data, e.g. the amount of production, consumption, international trade or producer and consumer prices, do not exist in most European countries. In some European countries there are only rough estimates of the levels of production and consumption. There is no standardization and data are seldom comparable. Furthermore, detailed information on specific commodities is missing. Hence, investment decisions are taken under conditions of great uncertainty. Likewise, if politicians want to support organic agriculture, they do not know whether it would be better to support production or consumption or to address problems in the marketing channel. The EU concerted action EISfOM (QLK5-2002-02400) (European Information System for Organic Markets) is attempting to take the first steps in solving these problems. The aim of this concerted action is to build up a framework for reporting valid and reliable data for relevant production and market sectors of the European organic sector in order to meet the needs of policy-makers, farmers, processors, wholesalers and other actors involved in organic markets. In order to reach this aim, this action was split into several workpackages. This report describes the approach and results of workpackages 2 and 3. In this first chapter the objective and general approach of these work packages are described. Chapters 2 and 3 provide an overview of international statistics and data collection systems within the food supply chain at the public and the private level. Chapter 4 describes national statistics and data collection systems within the food supply chain. In Chapter 5, an analysis and appraisal is made of the results with regard to organic data collection and processing systems (DCPSs) and their integration into existing common DCPSs. Chapter 6 draws several general conclusions. Two substantial annexes complete the report, one with the country reports on the situation of data collection and processing in all investigated countries and the other with the first and the second stage questionnaires covering the different data collection levels

Quarkonia Measurements with the Central Detectors of ALICE

A Large Ion Collider Experiment - ALICE will become operational with the startup of the Large Hadron Collider - LHC at the end of 2007. One focus of the physics program is the measurement of quarkonia in proton-proton and lead-lead collisions. Quarkonia states will be measured in two kinematic regions and channels: di-muonic decays will be measured in the forward region by the muon arm, the central part of the detector will measure di-electronic decays. The presented studies show the expected performance of the di-electron measurement in proton-proton and central lead-lead collisions.Comment: 6 pages, 7 figures, Proceedings of the QM 2006 poster sessio

The evolution of ageing in cooperative breeders

Cooperatively breeding animals live longer than their solitary counterparts. The traditional explanation for this is that cooperative breeding evolves more readily in long-lived species. Here, we reverse this argument and show that long lifespans are an evolutionary consequence of cooperative breeding. Natural selection favours a delayed onset of senescence in cooperative breeders, relative to solitary breeders, because cooperative breeders have a delayed age of first reproduction due to reproductive queueing. Especially long lifespans evolve in cooperative breeders with age-dependent reproductive queueing. Finally, we show that lower genetic relatedness among group members leads to the evolution of longer lifespans. This is because selection against higher mortality is weaker when mortality reduces competition between relatives. Our results link the evolutionary theory of ageing with kin selection theory, demonstrating that the evolution of ageing in cooperative breeders is driven by the timing of reproduction and kin structure within breeding territories