Cepheid parallaxes and the Hubble constant   总被引：1，自引：0，他引：1  

Floor van Leeuwen  Michael W. Feast  Patricia A. Whitelock  Clifton D. Laney 《Monthly notices of the Royal Astronomical Society》2007,379(2):723-737

Revised Hipparcos parallaxes for classical Cepheids are analysed together with 10 Hubble Space Telescope ( HST )-based parallaxes. In a reddening-free V , I relation we find that the coefficient of log  P is the same within the uncertainties in our Galaxy as in the Large Magellanic Cloud (LMC), contrary to some previous suggestions. Cepheids in the inner region of NGC 4258 with near solar metallicities confirm this result. We obtain a zero-point for the reddening-free relation and apply it to the Cepheids in galaxies used by Sandage et al. to calibrate the absolute magnitudes of Type Ia supernova (SNIa) and to derive the Hubble constant. We revise their result for H ₀ from 62 to 70 ± 5 km s⁻¹ Mpc⁻¹. The Freedman et al. value is revised from 72 to 76 ± 8 km s⁻¹ Mpc⁻¹. These results are insensitive to Cepheid metallicity corrections. The Cepheids in the inner region of NGC 4258 yield a modulus of 29.22 ± 0.03 (int.) compared with a maser-based modulus of 29.29 ± 0.15. Distance moduli for the LMC, uncorrected for any metallicity effects, are 18.52 ± 0.03 from a reddening-free relation in V , I ; 18.47 ± 0.03 from a period–luminosity relation at K ; 18.45 ± 0.04 from a period–luminosity–colour relation in J , K . Adopting a metallicity correction in V , I from Macri et al. leads to a true LMC modulus of 18.39 ± 0.05.  相似文献   

The host galaxies of long-duration gamma-ray bursts in a cosmological hierarchical scenario     

Sebastián E. Nuza  Patricia B. Tissera  Leonardo J. Pellizza  Diego G. Lambas  Cecilia Scannapieco †  María E. De Rossi 《Monthly notices of the Royal Astronomical Society》2007,375(2):665-672

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Welcome mats? The role of seagrass meadow structure in controlling post-settlement survival in a keystone sea-urchin species     

Patricia Prado  Javier Romero  Teresa Alcoverro 《Estuarine, Coastal and Shelf Science》2009

Processes acting on the early-life histories of marine organisms can have important consequences for the structuring of benthic communities. In particular, the degree of coupling between larval supply and adult abundances can wield considerable influence on the strength of trophic interactions in the ecosystem. These processes have been relatively well described in rocky systems and soft-sediment communities, and it is clear that they are governed by very different bottlenecks. Seagrass meadows make interesting study systems because they bear structural affinities to both soft sediments as well as rocky substrates. We examined the early-life history of Paracentrotus lividus, one of the dominant herbivores in Mediterranean seagrass meadows, to identify the drivers of population dynamics in this species. We measured spatial and temporal variability in sea urchin post-settlement in 10 Posidonia oceanica meadows in the North-Western Mediterranean over a period of two years, and compared the numbers with the one-year old cohort a year later (i.e. the new population recruitment) as well as between successive size–age groups. Urchin post-settlers differed substantially between meadows but were present in both years in all meadows surveyed, suggesting that larval supply was not limiting for any of the studied sites. However, in six of the studied meadows, the one-year cohort of urchins was absent in both years, indicating that post-settlement processes strongly affected urchins in these meadows. In contrast, in four of the studied meadows, there was a strong coupling between post-settlers and one-year cohort individuals. These meadows were structurally different from the others in that they were characterised by an exposed matrix of rhizomes forming a dense seagrass mat. This mat apparently strongly mediates post-settlement mortality, and its presence or absence dictates the successful establishment of urchin populations in seagrass meadows. As the population aged, the relationship between size–age groups decreased evidencing the action of other processes. Yet, these results indicate that differences in physical structure are a vital bottleneck for sea urchin populations in seagrass meadows. Exploring the interaction between ecosystem structure and early-life history may provide a broader and more unified framework to understand the dynamics of a range of benthic habitats, including rocky substrates, soft sediments and seagrass meadows.  相似文献   

Decline of brown trout (Salmotrutta) in Switzerland - how to assess potential causes in a multi-factorial cause-effect relationship.     

Patricia Burkhardt-Holm 《Marine environmental research》2008,66(1):181-182

A considerable decline in fish catch in Switzerland triggered a 5-year project (Fischnetz) to investigate potential causes. The results of many field and laboratory studies, together with literature and historical data, indicated a need for a concise synthesis of the results. Therefore, Bayesian probability network (BPN) and weight-of-evidence (WOE) approaches were applied. Here, these both approaches are compared and evaluated. In addition, the potential reasons for the (mis)match in the two approaches were evaluated. In both studies, proliferative kidney disease (PKD), caused by a parasite, and the clinical outbreak supported by various factors, was a very probable single parameter. WOE assessed habitat and streambed quality as likely for contributing to impaired health, recruitment and abundance at single sites only, but this parameter was assessed to be the most important and ubiquitous stressor in the BPN. Mismatches suggested that these factors were either not considered or not equally assessed by the different models, which is due to different endpoints, incomplete data sets and different handling of these various data sets by the applied synthesis approaches.  相似文献   

Paleoclimatic implications of glacial and postglacial refugia for Pinus pumila in western Beringia     

Patricia M. Anderson  Anatoly V. Lozhkin  Thomas A. Brown 《Quaternary Research》2010,73(2):269-276

Palynological results from Julietta Lake currently provide the most direct evidence to support the existence of a glacial refugium for Pinus pumila in mountains of southwestern Beringia. Both percentages and accumulation rates indicate the evergreen shrub survived until at least ∼ 19,000 ¹⁴C yr BP in the Upper Kolyma region. Percentage data suggest numbers dwindled into the late glaciation, whereas pollen accumulation rates point towards a more rapid demise shortly after ∼ 19,000 ¹⁴C yr BP. Pinus pumila did not re-establish in any great numbers until ∼ 8100 ¹⁴C yr BP, despite the local presence ∼ 9800 ¹⁴C yr BP of Larixdahurica, which shares similar summer temperature requirements. The postglacial thermal maximum (in Beringia ∼ 11,000-9000 ¹⁴C yr BP) provided Pinus pumila shrubs with equally harsh albeit different conditions for survival than those present during the LGM. Regional records indicate that in this time of maximum warmth Pinus pumila likely sheltered in a second, lower-elevation refugium. Paleoclimatic models and modern ecology suggest that shifts in the nature of seasonal transitions and not only seasonal extremes have played important roles in the history of Pinus pumila over the last ∼ 21,000 ¹⁴C yr BP.  相似文献   

Erratum to: Comparative Analysis of Phytoplankton Composition and Abundance over a Two-Decade Period at the Land<Emphasis Type="Italic">–</Emphasis>Ocean Boundary of a Tropical Mangrove Ecosystem     

Haimanti Biswas  Mitali Dey  Dipnarayan Ganguly  Tarun K. De  Sandip Ghosh  Tapan K. Jana 《Estuaries and Coasts》2010,33(2):395-398

Inter-annual variations of phytoplankton abundance and community organization were observed over a two-decade period along with the ancillary parameters at the land–ocean boundary associated with the Sundarban mangrove forest (21°32′ and 22°40′ N and 88°05′ and 89° E), along the NE Coast of the Bay of Bengal. The number of definable Bacillariophyceae species exceeded Dinophyceae taxa, and the total number of bloom-forming species declined from a maximum of ten in 2000 and a minimum of two in 2007. Blooms of the diatom Coscinodiscus radiatus were common in 2000 and 2007. Tide cycles and the onset of the monsoon season played important roles in diurnal and seasonal variability of phytoplankton. Phytoplankton biovolume showed seasonality, with the highest levels during post-monsoon periods and lowest levels during the monsoon period. Phytoplankton abundance was correlated to rainfall patterns, which may be altered by long-term changes in climate.  相似文献   

Using GIS to improve public health emergency response in rural areas during the COVID-19 crisis: A case study of South Carolina,US     

Patricia Carbajales-Dale  Dusti Annan-Coultas  Anjali Joseph  Martie Thompson  Roxana Jafarifiroozabadi  Susan P. Limber  Bonnie Holaday  Sahar Mihandoust 《Transactions in GIS》2023,27(4):975-995

Geographic information systems (GIS) have become essential tools in the public health domain, especially when it comes to monitoring and surveillance of disease. The purpose of this article is to describe and explore the benefits of using GIS to improve public health emergency response during a global pandemic and, in particular, how to effectively optimize the allocation of public health resources in a rural setting using a data-driven approach that considers the multifactorial demand for new COVID-19 testing sites. Herein, the authors present their interprofessional project as an example of such efforts to inform applications for practice. The team developed a GIS-based multicriteria decision analysis model for use by decision-makers and public health experts in similar future planning and response scenarios. Focus is placed on rural characteristics (e.g., accessibility), vulnerable populations, and daily changing conditions (e.g., COVID-19 daily case fluctuations) that create additional challenges for public health agencies and policymakers.  相似文献   

Effects of the large-scale atmospheric circulation on the onset and strength of urban heat islands: a case study     

Admir Créso Targino  Patricia Krecl  Guilherme Conor Coraiola 《Theoretical and Applied Climatology》2014,117(1-2):73-87

Air temperature was monitored at 13 sites across the urban perimeter of a Brazilian midsize city in winter 2011. In this study, we show that the urban heat island (UHI) develops only at night and under certain weather conditions, and its intensity depends not only on the site's land cover but also on the meteorological setting. The urban heat island intensity was largest (6.6 °C) under lingering high-pressure conditions, milder (3.0 °C) under cold anticyclones and almost vanished (1.0 °C) during the passage of cold fronts. The cooling rates were calculated to monitor the growth and decay of the UHI over each specific synoptic setting. Over four contiguous days under the effect of a lingering high-pressure event, we observed that the onset of cooling was always at about 2 h before sunset. The reference site attained mean cooling rate of ?2.6 °C h^?1 at sunset, whilst the maximum urban rate was ?1.2 °C h^?1. Under a 3-day cold anticyclone episode, cooling also started about 2 h before sunset, and the difference between maximum rural (?2.0 °C h^?1) and urban (?1.0 °C h^?1) cooling rates diminished. Under cold-front conditions, the cooling rate was homogeneous for all sites and swang about zero throughout the day. The air temperature has a memory effect under lingering high-pressure conditions which intensified the UHI, in addition to the larger heat storage in the urban area. Cold anticyclone conditions promoted the development of the UHI; however, the cold air pool and relatively light winds smoothed out its intensity. Under the influence of cold fronts, the urban fabric had little effect on the city's air temperature field, and the UHI was imperceptible.  相似文献   

Challenges to adaptation: a fundamental concept for the shared socio-economic pathways and beyond   总被引：1，自引：1，他引：0  

Dale S. Rothman  Patricia Romero-Lankao  Vanessa J. Schweizer  Beth A. Bee 《Climatic change》2014,122(3):495-507

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Nutrient Fluxes from Sediments in the San Francisco Bay Delta     

Jeffrey C. Cornwell  Patricia M. Glibert  Michael S. Owens 《Estuaries and Coasts》2014,37(5):1120-1133

In September 2011 and March 2012, benthic nutrient fluxes were measured in the San Francisco Bay Delta, across a gradient from above the confluence of the Sacramento and San Joaquin Rivers to Suisun Bay. Dark and illuminated core incubation techniques were used to measure rates of denitrification, nutrient fluxes (phosphate, ammonium, nitrate), and oxygen fluxes. While benthic nutrient fluxes have been assessed at several sites in northern San Francisco Bay, such data across a Delta–Bay transect have not previously been determined. Average September rates of DIN (nitrate, nitrite, ammonium) flux were net positive across all sites, while March DIN flux indicated net uptake of DIN at some sites. Denitrification rates based on the N₂/Ar ratio approach were between 0.6 and 1.0 mmol m^?2 day^?1, similar to other mesotrophic estuarine sediments. Coupled nitrification–denitrification was the dominant denitrification pathway in September, with higher overlying water nitrate concentrations in March resulting in denitrification driven by nitrate flux into the sediments. Estimated benthic microalgal productivity was variable and surprisingly high in Delta sediments and may represent a major source of labile carbon to this ecosystem. Variable N/P stoichiometry was observed in these sediments, with deviations from Redfield driven by processes such as denitrification, variable light/dark uptake of nutrients by microalgae, and adsorption of soluble reactive phosphorus.  相似文献