Near-IR age-dating of red supergiant-dominated stellar populations     

Ariane Lançon  Jay S. Gallagher  Moustapha Mouhcine  Linda J. Smith  Djazia Ladjal  Richard de Grijs 《Astrophysics and Space Science》2009,324(2-4):241-245

We present new spectral synthesis models for solar metallicity stellar populations, based on a library of stellar spectra that extends across near-IR wavelengths out to 2.4 µm at a resolution approaching 1000. We show that the spectra of massive star clusters in the starburst galaxy M 82 can be reproduced very well with these models. We compare near-IR spectroscopic ages with optical ages, and discuss the main sources of (systematic) errors that still affect those ages.  相似文献   

Mapping the roots of the galactic outflow in NGC1569     

Mark S. Westmoquette  Linda J. Smith  Jay S. Gallagher III  Katrina M. Exter 《Astrophysics and Space Science》2009,324(2-4):187-193

The exact nature of the interaction between hot, fast-flowing star-cluster winds and the surrounding clumpy interstellar medium (ISM) in starburst galaxies has very few observational constraints. Besides furthering our knowledge of ISM dynamics, detailed observations of ionised gas at the very roots of large-scale outflows are required to place limits on the current generation of high-resolution galactic wind models. To this end, we conduct a detailed investigation of the ionised gas environment surrounding the young star clusters in the starburst galaxy NGC1569. Using high spatial and spectral-resolution Gemini/GMOS integral-field unit observations, we accurately characterise the line-profile shapes of the optical nebular emission lines and find a ubiquitous broad (～300 km?s^?1) component underlying a bright narrower component. By mapping the properties of the individual line components, we find correlations that suggest that the broad component results from powerful cluster wind–gas clump interactions. We propose a model to explain the properties of the line components and the general turbulent state of the ISM.  相似文献   

Multiscale Analysis of Active Region Evolution     

R. J. Hewett  P. T. Gallagher  R. T. J. McAteer  C. A. Young  J. Ireland  P. A. Conlon  K. Maguire 《Solar physics》2008,248(2):311-322

Flows in the photosphere of solar active regions are turbulent in nature. Because magnetic fields are frozen into the plasma on the solar surface, magnetograms can be used to investigate the processes responsible for structuring active regions. Here, a continuous wavelet technique is developed, analyzed, and used to investigate the multiscale structure of an evolving active region using magnetograms obtained by the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO). The multiscale structure was measured using a 2D continuous wavelet technique to extract the energy spectrum of the region over the time scale of 13 days. Preliminary evidence of an inverse cascade in active region NOAA 10488 is presented as well as a potential relationship between energy scaling and flare productivity.  相似文献   

Historic nutrient loading and recent species invasions caused shifts in water quality and zooplankton demography in two Finger Lakes (New York, USA)     

Meghan E. Brown  Tara M. Curtin  Corey J. Gallagher  John D. Halfman 《Journal of Paleolimnology》2012,48(3):623-639

We investigated the paleolimnology of Owasco and Seneca Lakes (New York, USA) and compiled water-quality monitoring data to describe environmental change during the past two centuries. Trophic shifts were detected in the oligotrophic to mesotrophic range and were likely driven by nutrient loading and species invasion. Based on box core reconstructions, primary production increased in both lakes during the last century, which is evidenced by the amount, type and isotopic composition of material preserved in the sediment. Organic matter accumulation and its stable carbon isotopic composition, as well as carbonate abundance, began to increase during the 1960s in Owasco Lake and the 1850s in Seneca Lake. Further, the abundance of phytoplanktivorous cladocera subfossils increased beginning in the 1910s in Seneca Lake and in the 1960s in Owasco Lake. The different timing and magnitude of the trophic shifts likely resulted from contrasts in lake residence time and species assemblages between the two lakes. The increases in primary and secondary production paralleled, and are interpreted to reflect, increased allochthonous nutrient loading. However, nutrient loading was not detected in the water-quality data, perhaps because of strong uptake of phosphates by phytoplankton or due to limited data collection. Rapid changes in cladoceran subfossils and water quality were also detected during the last decade. Concurrent with the establishment of non-native Cercopagis pengoi (fishhook waterflea), phytoplanktivorous cladocera remains declined, and the mucrone length of Bosmina increased, consistent with predictions of increased invertebrate predation. Additionally, the post-1990 decline in sediment carbonate, increased Secchi depth and decreased chlorophyll a concentrations followed the establishment of filter-feeding Dreissena spp. (zebra and quagga mussels). Collectively, paleolimnological data and water-quality monitoring provided a more complete and consistent record of shifts in the productivity of Owasco and Seneca Lakes, which were useful to understand environmental changes over different time scales. Physical, geochemical and biological changes were temporally consistent among three cores collected from different locations in each lake, but differed in magnitude for several variables (e.g., grain size and cladoceran subfossils), which could reflect near-shore to offshore gradients.  相似文献   

Inference of past climate from borehole temperature data using Bayesian Reversible Jump Markov chain Monte Carlo     

Peter O. Hopcroft  Kerry Gallagher  Chris C. Pain 《Geophysical Journal International》2007,171(3):1430-1439

Estimates of past climate derived from borehole temperatures are assuming a greater importance in context of the millennial temperature variation debate. However, recovery of these signals is usually performed with regularization which can potentially lead to underestimation of past variation when noise is present. In this work Bayesian inference is applied to this problem with no explicit regularization. To achieve this Reversible Jump Markov chain Monte Carlo is employed, and this allows models of varying complexity (i.e. variable dimensions) to be sampled so that it is possible to infer the level of ground surface temperature (GST) history resolution appropriate to the data. Using synthetic examples, we show that the inference of the GST signal back to more than 500 yr is robust given boreholes of 500 m depth and moderate noise levels and discuss the associated uncertainties. We compare the prior information we have used with the inferred posterior distribution to show which parts of the GST reconstructions are independent of this prior information. We demonstrate the application of the method to real data using five boreholes from southern England. These are modelled both individually and jointly, and appear to indicate a spatial trend of warming over 500 yr across the south of the country.  相似文献   

Community respiration of decomposing plants in Oregon estuarine marshes     

John L. Gallagher  Harold V. Kibby  Katherine W. Skirvin 《Estuarine, Coastal and Shelf Science》1984,18(4):421-431

Community respiration rates in air and water were measured as indicators of the decomposition rate of dead plant tissue from nine stands of plants in two Oregon estuarine marshes. Respiration rates were low and relatively constant from November to February; during warmer periods several patterns emerged. The highest respiration rates for the most and least active communities differed up to one order of magnitude. The moisture, nitrogen, and crude fibre content, as well as plant shoot and canopy structure, appeared to be important determinants of the respiration rate. Comparisons of aerial and aquatic respiration rates for a single date may be useful for determining the recent moisture history of the tissue. Rates of dead plant community respiration in Pacific North-west marshes equalled and, in one case, exceeded those in the Atlantic South-east.  相似文献   

The resolution of past heat flow in sedimentary basins from non-linear inversion of geochemical data: the smoothest model approach, with synthetic examples   总被引：1，自引：0，他引：1  

Kerry Gallagher  Malcolm Sambridge 《Geophysical Journal International》1992,109(1):78-95

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A case study of stably stratified airflow over the pennines using an instrumented glider     

I. M. Stromberg  C. S. Mill  T. W. Choularton  M. W. Gallagher 《Boundary-Layer Meteorology》1989,46(1-2):153-168

In this paper we present data gathered during a weak case of the Helm wind, an example of supercritical airflow, in the vicinity of Cross Fell in Northern England. Airborne measurements have been made using an instrumented glider with simultaneous ground-based measurements both on a hill summit and on the valley floor downwind of the hill.It is found that the major features of the airflow both near the surface and aloft, including the lee-wave activity are well reproduced by the airflow model of Carruthers and Choularton (1982). Secondary features including several higher modes of lee-waves and changes in the valley flow associated with nocturnal cooling were observed which could not be accounted for by the simple model.  相似文献   

A generalized least-squares family of algorithms for transient dynamic analysis     

Jerzy Kujawski  Richard H. Gallagher 《地震工程与结构动力学》1989,18(4):539-550

By use of the generalized least-squares procedure, in conjunction with a finite element approximation in time, a simple three-time-level family of time integration schemes is derived. This results in fourth-order accurate unconditionally stable algorithms and stable eighth-order accurate non-dissipative algorithms. Numerical examples show the accuracy of the proposed schemes in comparison with the Fox-Goodwin formula and Newmark's average acceleration method.  相似文献   

Diurnal and seasonal variations of meteorology and aerosol concentrations in the foothills of the nepal himalayas (Nagarkot: 1,900 m asl)     

Rudra K. Shrestha  Martin W. Gallagher  Paul J. Connolly 《Asia-Pacific Journal of Atmospheric Sciences》2016,52(1):63-75

A 10-months long monitoring experiment to investigate the diurnal and seasonal variation of aerosol size distribution at Nagarkot (1,900 m asl) in the Kathmadu Valley was carried out as part of a study on katabatic and anabatic influence on pollution dispersion mechanisms. Seasonal means show total aerosol number concentration was highest during post-monsoon season (775 ± 417 cm^?3) followed by pre-monsoon (644 ± 429 cm^?3) and monsoon (293 ± 205 cm^?3) periods. Fine particle concentration (0.25 μm ≤ D_P ≤ 2.5 μm) dominated in all seasons, however, contribution by coarse particles (3.0 μm ≤ D_P ≤ 10.0 μm) is more significant in the monsoon season with contributions from particles larger than 10.0 μm being negligible. Our results show a regular diurnal pattern of aerosol concentration in the valley with a morning and an evening peak. The daily twin peaks are attributed to calm conditions followed by transitional growth and break down of the valley boundary layer below. The peaks are generally associated with enhancement of the coarse particle fraction. The evening peak is generally higher than the morning peak, and is caused by fresh evening pollution from the valley associated with increased local activities coupled with recirculation of these trapped pollutants. Relatively clean air masses from neighbouring valleys contribute to the smaller morning peak. Gap flows through the western passes of the Kathmandu Valley, which sweep away the valley pollutants towards the eastern passes modulated by the mountain - valley wind system, are mainly responsible for the dominant pollutant circulation patterns exhibited within the valley.  相似文献