3 resultados para Branching Processes with Immigration
Resumo:
This article introduces the first findings of the Political Party Database Project, a major survey of party organizations in parliamentary and semi-presidential democracies. The project’s first round of data covers 122 parties in 19 countries. In this article, we describe the scope of the database, then investigate what it tells us about contemporary party organization in these countries, focusing on parties’ resources, structures and internal decision-making. We examine organizational patterns by country and party family, and where possible we make temporal comparisons with older data sets. Our analyses suggest a remarkable coexistence of uniformity and diversity. In terms of the major organizational resources on which parties can draw, such as members, staff and finance, the new evidence largely confirms the continuation of trends identified in previous research: that is, declining membership, but enhanced financial resources and more paid staff. We also find remarkable uniformity regarding the core architecture of party organizations. At the same time, however, we find substantial variation between countries and party families in terms of their internal processes, with particular regard to how internally democratic they are, and the forms that this democratization takes.
Resumo:
Collisionless shocks, that is shocks mediated by electromagnetic processes, are customary in space physics and in astrophysics. They are to be found in a great variety of objects and environments: magnetospheric and heliospheric shocks, supernova remnants, pulsar winds and their nebulæ, active galactic nuclei, gamma-ray bursts and clusters of galaxies shock waves. Collisionless shock microphysics enters at different stages of shock formation, shock dynamics and particle energization and/or acceleration. It turns out that the shock phenomenon is a multi-scale non-linear problem in time and space. It is complexified by the impact due to high-energy cosmic rays in astrophysical environments. This review adresses the physics of shock formation, shock dynamics and particle acceleration based on a close examination of available multi-wavelength or in situ observations, analytical and numerical developments. A particular emphasis is made on the different instabilities triggered during the shock formation and in association with particle acceleration processes with regards to the properties of the background upstream medium. It appears that among the most important parameters the background magnetic field through the magnetization and its obliquity is the dominant one. The shock velocity that can reach relativistic speeds has also a strong impact over the development of the micro-instabilities and the fate of particle acceleration. Recent developments of laboratory shock experiments has started to bring some new insights in the physics of space plasma and astrophysical shock waves. A special section is dedicated to new laser plasma experiments probing shock physics.
Resumo:
A selected ion flow tube study of the reactions of a series of gas-phase atomic cations (S+, Xe+, O+, Kr+, N+, Ar+ and Ne+) and molecular ions (SF n+ (n = 1-5), CFn+ (n = 1-3), CF2Cl+, H3O+, NO+, N 2O+, CO2+, CO+, and N2+) spanning a large range of recombination energies (6.3-21.6 eV), with acetone, 1,1,1-trifluoroacetone, and hexafluoroacetone has been undertaken with the objective of exploring the nature of the reaction ion chemistry as the methyl groups in acetone are substituted for CF3. The reaction rate coefficients and product ion branching ratios for all 66 reactions, measured at 298 K, are reported. The experimental reaction rate coefficients are compared to theoretically calculated collisional values. Several distinct reaction processes were observed among the large number of reactions studied, including charge transfer (non-dissociative and dissociative), abstraction, ion-molecule associations and, in the case of the reactions involving the reagent ion H3O+, proton transfer.