ABSTRACT
We made a survey of the variable stars in a 13.2 × 13.2 arcmin$^{2}$ centred on the field of the Galactic bulge cluster NGC 6558. A total of 78 variables were found in the field of the ...cluster. Many of these variables are included in the catalogue of variable stars in Galactic globular clusters (Clement et al. 2001), OGLE or Gaia DR3 data releases. A membership analysis based on the proper motions of Gaia DR3 revealed that many of these variables do not belong to the cluster. We employed the data from the aforementioned surveys and our own data in the VI photometric system to estimate the periods, which along with the light-curves morphology and position in a deferentially dereddened colour–magnitude diagram (CMD), help classifying the variable types. Two new member variables were found; an eclipsing binary (V18) and a semiregular SR/L (V19). In the end, we conclude that only nine variables are likely cluster members. Member variables were used to discuss the mean metallicity and distance of the parental cluster and find the average values.
Geologic reservoirs containing gas hydrate occur beneath permafrost environments and within marine continental slope sediments, representing a potentially vast natural gas source. Numerical ...simulators provide scientists and engineers with tools for understanding how production efficiency depends on the numerous, interdependent (coupled) processes associated with potential production strategies for these gas hydrate reservoirs. Confidence in the modeling and forecasting abilities of these gas hydrate reservoir simulators (GHRSs) grows with successful comparisons against laboratory and field test results, but such results are rare, particularly in natural settings. The hydrate community recognized another approach to building confidence in the GHRS: comparing simulation results between independently developed and executed computer codes on structured problems specifically tailored to the interdependent processes relevant for gas hydrate-bearing systems. The United States Department of Energy, National Energy Technology Laboratory, (DOE/NETL), sponsored the first international gas hydrate code comparison study, IGHCCS1, in the early 2000s. IGHCCS1 focused on coupled thermal and hydrologic processes associated with producing gas hydrates from geologic reservoirs via depressurization and thermal stimulation. Subsequently, GHRSs have advanced to model more complex production technologies and incorporate geomechanical processes into the existing framework of coupled thermal and hydrologic modeling.
This paper contributes to the validation of these recent GHRS developments by providing results from a second GHRS code comparison study, IGHCCS2, also sponsored by DOE/NETL. IGHCCS2 includes participants from an international collection of universities, research institutes, industry, national laboratories, and national geologic surveys. Study participants developed a series of five benchmark problems principally involving gas hydrate processes with geomechanical components. The five problems range from simple geometries with analytical solutions to a representation of the world's first offshore production test of methane hydrates, which was conducted with the depressurization method off the coast of Japan. To identify strengths and limitations in the various GHRSs, study participants submitted solutions for the benchmark problems and discussed differing results via teleconferences. The GHRSs evolved over the course of IGHCCS2 as researchers modified their simulators to reflect new insights, lessons learned, and suggested performance enhancements. The five benchmark problems, final sample solutions, and lessons learned that are presented here document the study outcomes and serve as a reference guide for developing and testing gas hydrate reservoir simulators.
•Code comparisons build confidence in simulators to model interdependent processes.•International hydrate reservoir simulators are compared over five complex problems.•Geomechanical processes significantly impact response of gas hydrate reservoirs.•Simulators yielded comparable results, however many differences are noted.•Equivalent constitutive models are required to achieve agreement across simulators.
Ammonia volatilization losses from surface applied urea could reduce the N-use efficiency in loblolly pine (Pinus taeda L.) plantations. Three field studies were conducted to assess the effectiveness ...of two urea formulations: coated-urea fertilizer (CUF) and the urease inhibitor N-(n-butyl) thiophosphoric triamide-treated urea (NBPT) at reducing ammonia (NH3) losses in loblolly pine plantations under different forest floor moisture (dry vs. wet), substrate (forest floor vs. mineral soil), and site/soil type conditions (Piedmont vs. Coastal Plain). An additional laboratory study under controlled environmental conditions helped validate the results from the field. Ammonia volatilization losses were influenced more by the initial forest floor moisture than by the fertilizer formulations and were 43% lower when the fertilizer treatments were applied directly on the forest floor than on the exposed mineral soil. The average NH3 losses, expressed as a percentage of applied N, in the Piedmont ranged from 1 to 9%, and from 7 to 16%, 7 and 30 d after fertilization, respectively. At Day 7, both CUF and NBPT reduced NH3 losses, as compared with untreated urea, by 39 and 80%, respectively. In the Coastal Plain, NH3 losses ranged from 7 to 17%, 7 d after fertilization. Both CUF and NBPT reduced NH3 losses, as compared with untreated urea, by 35 and 25%, respectively. This difference in treatment ranking between sites suggests a fertilizer by site/soil type interaction which the laboratory study confirmed. These results highlight the importance of knowing the environmental and site conditions before fertilization and can help decide where and when these formulations might be used more effectively.
The effects of varying forest floor and slash retention at time of regeneration were evaluated 10 years after the establishment of a loblolly pine plantation near Millport, Alabama. Treatments ...included removing, leaving unaltered, or doubling the forest floor and slash material. Forest floor and litterfall mass and nutrient concentrations, available soil N, foliar nutrient concentrations and stand yield were all impacted by the treatments. Forest floor mass and nutrient contents in the doubled treatment were significantly greater than the other two treatments. The doubled treatment accumulated 25, 45 and 350% more forest floor mass and 56, 56, and 310% more N than the control treatment in the Oi, Oe, and Oa layers, respectively. The other nutrients followed similar patterns. Potentially mineralized NO
3
−-N in the mineral soil was also significantly higher in the doubled treatment. The positive effect of doubling the forest floor on soil N availability was reflected in greater foliage production, 30% more litterfall and 25% more stand yield for this treatment. This study shows that increasing the forest floor retention has resulted in increased nutrient availability and improved tree growth.
•Loblolly pine forests managed for woody and herbaceous bioenergy production.•Switchgrass intercropped between bedded rows of pine trees.•Soil NH4+ and NO3- concentrations reduced under ...switchgrass.•Elevated NO3- concentrations in pine beds adjacent to switchgrass.•Switchgrass utilized soil N when N supply was greater than pine N demand.
As biofuel production continues to increase, so will demand for forests to provide sources of biomass feedstocks. Intensively managed loblolly pine (Pinus taeda L.) plantations cover 15.8 million ha of the southeastern United States. Intercropping of switchgrass (Panicum virgatum L.) within loblolly pine stands offers an opportunity to use interbed space to produce an herbaceous biomass feedstock. Furthermore, removal of post-harvest woody residues could act as another forest-based biomass feedstock. Understanding how managing forests for biofuel production influences soil nitrogen (N) cycling and availability is crucial given the critical role N plays in terrestrial ecosystem productivity. Therefore, our objective was to study effects of harvest residue removal and pine-switchgrass intercropping on soil extractable NH4+ and NO3-. We used a randomized complete block design, consisting of four blocks of seven plots (0.8ha) established in the summer of 2008 on a recently harvested 34-year-old loblolly pine plantation in the Lower Coastal Plain of North Carolina, USA. Ion exchange membranes were deployed in the top 10cm of mineral soil starting in June 2009 and replaced continuously every 4–6weeks through December 2011. Presence of switchgrass significantly reduced soil extractable NH4+ and NO3-, amounting to a total reduction of 39% and 60%, respectively, over the course of the timeframe (30months) of this study. There was evidence that intercropping of switchgrass increased extractable NO3- in the adjacent pine bed, although this result was only found in the final 6months of the study. Presence or absence of harvest residues and/or interbed pines in the interbeds generally had no effect on soil inorganic N pools. These results indicate that switchgrass production effectively utilized inorganic N during a time when mineral N supply was greater than N demand by loblolly pines. Assessment of the long-term effects of switchgrass intercropping on soil nutrient cycling and availability and pine health and productivity will be essential to determine environmental and economic sustainability of intercropping.
The synchronization of nutrient release and demand in early stand establishment is important to maximizing resource use in forest plantations. We explored the impacts of forest floor manipulations on ...the dynamics of forest floor and mineral soil nutrient pools in a Pinus taeda L. plantation in North Carolina prior to and during 2 years following harvest and replanting. We present a novel method to estimate forest floor decomposition that avoids the exclusion of large detritivores. Decomposition and nutrient release rates from the forest floor were higher than rates typically observed in older stands (averaging 81% mass loss and 75% N loss across treatments over the 2-year period), highlighting the potential importance of the forest floor nutrient pool in early stand nutrition. Doubling the forest floor increased available C, N, and P pools in the mineral soil 46%, 47%, and 49%, respectively. Incorporating the forest floor into mineral soil through mixing had only transient positive effects on nutrient pools. Across treatments, an expected postharvest flush of soil available N was observed; however, removing the forest floor caused an earlier flush of available N in comparison with the control treatment, and doubling the forest floor caused a year delay in maximum N availability, better synchronizing the siteâs available N with stand demand.
Reportamos el caso de un varón de 54 años portador de VHC y VIH estadio SIDA quien tuvo hepatitis granu-lomatosa y frotis de sangre positivo a Paracoccidioides brasiliensis concomitante al hallazgo ...de Mycobacterhim tuberculosis multiresistente en esputo, que evolucionó con reactivación de citomegalovirus (pancreatitis probable y retinitis). Se describen las dificultades diagnósticas y terapéuticas en un paciente con múltiples infecciones.
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