Changes in the northern Gulf of St. Lawrence ecosystem estimated by inverse modelling: Evidence of a fishery-induced regime shift?

Mass-balance models have been constructed using inverse methodology for the northern Gulf of St. Lawrence for the mid-1980s, the mid-1990s, and the early 2000s to describe ecosystem structure, trophic group interactions, and the effects of fishing and predation on the ecosystem for each time period. Our analyses indicate that the ecosystem structure shifted dramatically from one previously dominated by demersal (cod, redfish) and small-bodied forage (e.g., capelin, mackerel, herring, shrimp) species to one now dominated by small-bodied forage species. Overfishing removed a functional group in the late 1980s, large piscivorous fish (primarily cod and redfish), which has not recovered 14 years after the cessation of heavy fishing. This has left only marine mammals as top predators during the mid-1990s, and marine mammals and small Greenland halibut during the early 2000s. Predation by marine mammals on fish increased from the mid-1980s to the early 2000s while predation by large fish on fish decreased. Capelin and shrimp, the main prey in each period, showed an increase in biomass over the three periods. A switch in the main predators of capelin from cod to marine mammals occurred, while Greenland halibut progressively replaced cod as shrimp predators. Overfishing influenced community structure directly through preferential removal of larger-bodied fishes and indirectly through predation release because larger-bodied fishes exerted top-down control upon other community species or competed with other species for the same prey. Our modelling estimates showed that a change in predation structure or flows at the top of the trophic system led to changes in predation at all lower trophic levels in the northern Gulf of St. Lawrence. These changes represent a case of fishery-induced regime shift.     

Multi-thermal observations of newly formed loops in a dynamic flare

The dynamic flare of 6 November, 1980 (max 15:26 UT) developed a rich system of growing loops which could be followed in H for 1.5 hr. Throughout the flare, these loops, near the limb, were seen in emission against the disk. Theoretical computations of deviations from LTE populations for a hydrogen atom reveal that this requires electron densities in the loops close to, or in excess of 10¹² cm ^-3. From measured widths of higher Balmer lines the density at the tops of the loops was found to be 4 x 10¹² cm ^-3 if no non-thermal motions were present, or 5 × 10¹¹ cm ^-3 for a turbulent velocity of ~ 12 km s ^-1.It is now general knowledge that flare loops are initially observed in X-rays and become visible in H only after cooling. For such a high density, a loop would cool through radiation from 10⁷ to 10⁴ K within a few minutes so that the dense H loops should have heights very close to the heights of the X-ray loops. This, however, contradicts the observations obtained by the HXIS and FCS instruments on board SMM which show the X-ray loops at much higher altitudes than the loops in H. Therefore, we suggest that the density must have been significantly lower when the loops were formed and that the flare loops were apparently both shrinking and increasing in density while cooling.NAS/NRC Research Associate, on leave from CNIE, Argentina.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. Partial support for the National Solar Observatory is provided by the USAF under a Memorandum of Understanding with the NSF.     

The origin of galactic magnetic fields

In this article it is argued that galactic magnetic fields are generated in the earliest moments of galaxy collapse. Our model proposes that provided, even if only briefly, a supermassive star is formed early on in the galaxy formation process, this star can produce a strong centrally localized magnetic field which may act as the seed field from which a galactic field can grow. In order to substantiate this model, detailed numerical calculations will be required.     

Tidal circularization in massive binaries

We consider the time-scale of orbital circularization for those massive binary systems that produce WR+C systems. Using the observation that such systems have acquired circular orbits on a time-scale of the order of the Main-Sequence lifetime of the initial secondary, we estimate the intrinsic time-scale of the tidal interaction ₀. We find that the tidal dissipation in such systems is very efficient and that, on the average, ₀ ~ 10³ yr.     

A fast technique for improved 3-dimensional mapping of the solar corona

To obtain improved maps of the coronal electron density distribution we have devised an iterative technique in which an approximation of the unknown distribution is successively modified to reduce discrepancies with the original data. With this technique we can now map the corona to a much finer resolution than shown in our previous papers, without greatly increasing the computational cost. The series representation of density may now contain more than 23 000 terms compared with previous limit of 128. This results in a fourfold increase in linear resolution, so that features about a tenth of a solar radius in width are now separated. The iteration algorithm can be adjusted to apply a mathematically optimal correction to a given approximation of the density. Although this correction minimizes noise levels, a cheaper version of the algorithm yields a better result.     

Mass motions associated with solar flares

Mass motions are a principal means by which components of solar flares can be distinguished. Typical patterns of mass motions in H are described for chromospheric flare ribbons, remote chromospheric flare patches, flare loops, flaring arches, surges, erupting filaments and some expanding coronal features. Interrelationships between these phenomena are discussed and illustrations of each are presented.     

A note on the problem of choosing a model of the Universe,III

From the analysis of relativistic and quantum-mechanical processes at the creation of the expansive evolution phase of the Universe it follows that the Universe can expand only by the limit velocity of signal propagationc.     

The spatial stability of alcohol outlets and crime in post‐disaster Christchurch,New Zealand

The devastating Canterbury Earthquakes of 2010 and 2011 left an indelible mark on the city of Christchurch. The social and economic upheaval that immediately followed the Earthquakes has, in time, been replaced with a period of rebuild and transformation. In this study we investigate the effects that the Canterbury Earthquakes had on two important and inter‐related phenomena in the city: alcohol availability and crime. More specifically, we investigate how alcohol outlets and crime across six different categories changed in magnitude and spatial distribution pre‐ (end‐2009) and post‐ (end‐2014) earthquake. We do this using a variety of geospatial techniques including a relatively new method: the spatial point pattern test which allows for the identification of changes in spatial patterns at the local level. Results indicate that both alcohol outlets and crime have decreased in magnitude since the Canterbury Earthquakes. Using the spatial point pattern test we found statistically significant differences in spatial point patterns for both alcohol outlets and all crime types pre‐ to post‐earthquake. The similarity in the differences of the spatial distributions of alcohol outlets and crime provides a first empirical clue of their potential association in the city post‐earthquake.