Gamma Echo Interpreted as a Phase-Shift Induced Transparency

In the gamma-echo technique a radioactive source is moved, with respect to a nuclear-resonant absorber, during the lifetime of first-excited nuclear state. This introduces a phase shift between the source radiation and the radiation from the absorber. If the source is moved abruptly, introducing a pi phase shift, the time-dependent intensity shows a sharp increase in the intensity at that time, the gamma echo. Using the recently developed one-dimensional quantum-mechanical model, based on the technique developed by Heitler and Harris, the gamma-echo effect is seen to be a phase-shift-induced transparency. A closed-form solution for the time-dependent transmitted intensity has been obtained. The solution has the form of a sum over coherent paths that the radiation takes in going from the radioactive source through the absorber to the detector. The model shows that the sharp increase in the intensity, the gamma echo, at the time when the source is moved abruptly is due to constructive interference, starting at that time, between the source radiation and the radiation from the absorber. The exact. form of the gamma-echo spectrum depends on the movement of the source. Shapes having multiple peaks are possible. All shapes can be found using the one-dimensional model

Comment on On the Theory of Nuclear Resonant Forward Scattering of Synchrotron Radiation

Recently, in a paper by Kohn and Smirnov, a formula previously derived by Kagan et al. was developed to explain the forward scattering of gamma radiation by a nuclear-resonant sample excited by pulsed synchrotron radiation. Their derivation followed, directly, a procedure developed by Heitler, Harris, and Hoy. Previously, a completely different formula was developed by Hoy et al. to explain the same process. As a result, Kohn and Smirnov discuss the correctness and validity of the two models. In this Comment a detailed numerical comparison of the two theories has also been made. It is shown that their comparison is substantially inaccurate. The two models give essentially the same results. There is some small difference at times long after the synchrotron radiation pulse. If experiments of this type are used to extract nuclear parameters, either model will provide the same results. Either model will fit the experimental data well

Techniques to Understand Computer Simulations: Markov Chain Analysis

The aim of this paper is to assist researchers in understanding the dynamics of simulation models that have been implemented and can be run in a computer, i.e. computer models. To do that, we start by explaining (a) that computer models are just input-output functions, (b) that every computer model can be re-implemented in many different formalisms (in particular in most programming languages), leading to alternative representations of the same input-output relation, and (c) that many computer models in the social simulation literature can be usefully represented as time-homogeneous Markov chains. Then we argue that analysing a computer model as a Markov chain can make apparent many features of the model that were not so evident before conducting such analysis. To prove this point, we present the main concepts needed to conduct a formal analysis of any time-homogeneous Markov chain, and we illustrate the usefulness of these concepts by analysing 10 well-known models in the social simulation literature as Markov chains. These models are: • Schelling\'s (1971) model of spatial segregation • Epstein and Axtell\'s (1996) Sugarscape • Miller and Page\'s (2004) standing ovation model • Arthur\'s (1989) model of competing technologies • Axelrod\'s (1986) metanorms models • Takahashi\'s (2000) model of generalized exchange • Axelrod\'s (1997) model of dissemination of culture • Kinnaird\'s (1946) truels • Axelrod and Bennett\'s (1993) model of competing bimodal coalitions • Joyce et al.\'s (2006) model of conditional association In particular, we explain how to characterise the transient and the asymptotic dynamics of these computer models and, where appropriate, how to assess the stochastic stability of their absorbing states. In all cases, the analysis conducted using the theory of Markov chains has yielded useful insights about the dynamics of the computer model under study.Computer Modelling, Simulation, Markov, Stochastic Processes, Analysis, Re-Implementation

Earnings and wealth inequality and income taxation: quantifying the tradeoffs of switching to a proportional income tax in the U.S.

This paper quantifies the steady-state aggregate, distributional, and mobility effects of switching the U.S. to a proportional income tax system.Income tax

Genetic structure of Balearic honeybee populations based on microsatellite polymorphism

The genetic variation of honeybee colonies collected in 22 localities on the Balearic Islands (Spain) was analysed using eight polymorphic microsatellite loci. Previous studies have demonstrated that these colonies belong either to the African or west European evolutionary lineages. These populations display low variability estimated from both the number of alleles and heterozygosity values, as expected for the honeybee island populations. Although genetic differentiation within the islands is low, significant heterozygote deficiency is present, indicating a subpopulation genetic structure. According to the genetic differentiation test, the honeybee populations of the Balearic Islands cluster into two groups: Gimnesias (Mallorca and Menorca) and Pitiusas (Ibiza and Formentera), which agrees with the biogeography postulated for this archipelago. The phylogenetic analysis suggests an Iberian origin of the Balearic honeybees, thus confirming the postulated evolutionary scenario for Apis mellifera in the Mediterranean basin. The microsatellite data from Formentera, Ibiza and Menorca show that ancestral populations are threatened by queen importations, indicating that adequate conservation measures should be developed for protecting Balearic bees

Governance of inter-organizational systems: a longitudinal case study of Rotterdam’s Port Community System

An increasing use of inter-organizational systems, as Port Community System (PCS), can be observed in port collaborations. As multiple organizations often rely on PCS, even for business-critical processes, proper governance of these systems is crucial. This study aims to explain the governance of inter-organizational port collaborations using a lifecycles paradigm. The governance is explored using three points of view – i.e. governance mechanisms, governance aspects, and governance models – and by describing the actors’ roles in collaborations. A case study in the port of Rotterdam is analyzed to explain how these actors affect the governance models through the mechanisms to govern the aspects in each lifecycle stage. The port collaboration in Rotterdam has gone through three full governance lifecycles and has entered the fourth iteration after the set-up of Portbase. During the last two cycles, the collaboration has maintained its Network Administrative Organization governance model. This case study analysis of Rotterdam’s port collaboration provides an example of how a systematic approach could help to discuss and communicate the governance of inter-organizational port collaboration systems and gives some lessons learned for other collaborations