Winds from clusters with non-uniform stellar distributions

We present the analytic and numerical models of the 'cluster wind' resulting from the multiple interactions of the winds ejected by the stars of a dense cluster of massive stars. We consider the case in which the distribution of stars (i.e. the number of stars per unit volume) within the cluster is spherically symmetric, has a power-law radial dependence, and drops discontinuously to zero at the outer radius of the cluster. We carry out comparisons between an analytic model (in which the stars are considered in terms of a spatially continuous injection of mass and energy) and 3D gasdynamic simulations (in which we include 100 stars with identical winds, located in 3D space by statistically sampling the stellar distribution function). From the analytic model, we find that for stellar distributions with steep enough radial dependencies, the cluster wind flow develops a very high central density and a non-zero central velocity, and for steeper dependencies, it becomes fully supersonic throughout the volume of the cluster (these properties are partially reproduced by the 3D numerical simulations). Therefore, the wind solutions obtained for stratified clusters can differ dramatically from the case of a homogeneous stellar distribution (which produces a cluster wind with zero central velocity, and a fully subsonic flow within the cluster radius). Finally, from our numerical simulations, we compute predictions of X-ray emission maps and luminosities, which can be directly compared with observations of cluster wind flows.     

CME Classification Based on Wavelet Spectra

We study the internal structure of coronal mass ejections (CMEs) using wavelet analysis. We derive wavelet spectra, spatially integrated over regions of interest within LASCO C2 white-light coronographic images. These spectra show an inflection point, which we use to characterize each spectrum. In a diagram of flux vs. spatial scale of the inflection point, we find that the analyzed structures fall into two, distinct groups: a low-flux, small-spatial-scale group (which we call the “homogeneous” type), and a high-flux, larger-spatial-scale group (the “collimated” type). Interestingly, if we study different regions of a given image, all of the structures fall into one of the two groups described above. From a qualitative comparison with the images, it is clear that the two groups identified by the wavelet analysis correspond to two types of morphologies, which are seen as either more-homogeneous or more-collimated structures.     

The age and growth of hottentot seabream Pachymetopon blochii before and after the South African linefish state of emergency in 2000

The hottentot seabream Pachymetopon blochii is a small-sized (maximum 2.67 kg) sparid endemic to southern Africa. It is an important target in South Africa's Western Cape traditional linefishery, particularly in the absence of more valuable pelagic species (such as Thyrsites atun and Seriola lalandi). In 2000, South Africa's linefishery was declared to be in a state of emergency, and commercial fishing effort was consequently reduced by 70%. A subsequent increase in stock biomass and intraspecific competition, coupled with environmental changes, were hypothesised to have thereafter altered the growth rate of hottentot, from 2000 to 2010. This study aimed to revise outdated age–growth models for the hottentot by using modern techniques (sectioned otoliths), and to compare age–growth relationships before and after the declared linefish state of emergency. The maximum age observed was 19 years, with no difference in the growth rate between sexes (p = 0.39–0.43) or time-periods (p = 0.96). Although the growth rate did not change, there is evidence that the age structure of the stock changed between time-periods as a result of changes in fishing pressure between 2000 and 2010. The enhanced recent growth model for hottentot, described as L_t = 418.063 (1 – e^{?0.104(t – [?4.709])}) (pooled sexes; n = 206), indicates a considerably slower growth rate for this species than was proposed previously using whole otoliths and has major implications for effective stock management.     

Coupled stellar jet/molecular outflow models

Molecular outflows can be modelled as environmental material entrained into high velocity stellar jets. Even though models of this entrainment process are at this time quite uncertain, a few preliminary theoretical efforts have been made. Three different models are discussed, in which the molecular outflows are identified with the turbulent mixing layer at the edge of a jet, with a turbulent envelope (driven by a large number of internal working surfaces in the jet) and with the wake of one working surface.     

Population ecology of Sinelobus stanfordi (Crustacea: Tanaidacea) in a temperate southern microtidal estuary

Sinelobus stanfordi is a tanaidacean of worldwide distribution of considerable significance within coastal ecosystems. The aim of this research was to provide essential information on the poorly-known population biology of this species. Benthic samples were taken seasonally from winter 2005 through summer 2007 along 155?km of shoreline within the Río de la Plata Estuary, Argentina. The density of this tanaidacean was higher in vegetated than in bare sediments. The smaller individuals flourished in spring and summer, whereas the larger mature members prevailed in the cooler seasons. Females were always twice as abundant as males. Copulatory females, with 18?±?8 eggs each, were collected during all the seasons. Five cohorts were distinguished by the von Bertalanffy growth function. This research represents a baseline investigation for future studies on the population dynamics of S. stanfordi both in this estuary and in other places where this species is found.     

A new plasmon solution with centrifugal pressure

The 'plasmon' solution of De Young & Axford describes the interaction between a high-velocity clump and the surrounding medium. Even though this solution is probably too simplistic, it has proven to be most useful in the study of diverse astrophysical flows. In the present paper, we discuss a more detailed solution of the plasmon problem, which includes the centrifugal effects of the environmental material flowing around the plasmon. We derive both numerical and approximate analytic solutions of this problem, and compare them with the analytic solution of De Young & Axford.     

Changes in extended boreal summer tropical cyclogenesis associated with large-scale flow patterns over the western North Pacific in response to the global warming hiatus

Climate Dynamics - This study examines extended boreal summer (May–October) tropical cyclogenesis events (TCGEs) associated with large-scale flow patterns (LFPs) over the western North...     

The motion of wind-driven shells

We present a method for solving problems in which a stellar wind interacts with the surrounding environment through the production of a 'double radiative shock' structure. This condition is generally met in problems involving winds ejected from young stars. We describe a method that can be applied to problems of winds with arbitrary time and angular dependence, interacting with a stationary environment with an arbitrary density distribution. We apply the method to the interaction of: a steady wind (with an instantaneous 'turning-on') with a power-law environmental density stratification, a 'wind plus jet' ejection with a toroidal environmental density stratification, and to the interaction of an isotropic wind with a clumpy environment. These three examples illustrate the wide range of possible applications of the proposed method. We also show a comparison between some of our thin-shell solutions and three-dimensional isothermal gasdynamic simulations of the flows. These comparisons are used as an evaluation of the applicability of our thin-shell solutions to the real flows.     

Jets and Narrow Line Cloud Formation in Seyfert Galaxies

In this paper we present simulations of an extragalactic jet interacting with a clumpy and filamentary narrow line region (NLR) similar to the one observed in NGC 1068. We study the kinematic disturbance produced by the interaction. Hα recombination emissivity maps and the spectral distribution of the emission are calculated. We find that ablation flows from high density clouds in the turbulent cocoon can produce fast, high emissivity flows, resulting in line widths of the order of 1000 km s-1 comparable to those observed in NGC 1068 and other Seyfert galaxies with radio ejecta.