A uniform solution of the Lambert problem

A uniform method (with respect to the type of the conic section) for solving the Lambert boundary value problem is presented. It is derived by using the KS-transformation and consists in solving one nonlinear equation. It can be used either in the ordinaryx-frame (physical space) as well as in the KS-coordinates (regularized space).     

Radium uptake during barite recrystallization at 23 ± 2 °C as a function of solution composition: An experimental Ba and Ra tracer study

High-purity synthetic barite powder was added to pure water or aqueous solutions of soluble salts (BaCl₂, Na₂SO₄, NaCl and NaHCO₃) at 23 ± 2 °C and atmospheric pressure. After a short pre-equilibration time (4 h) the suspensions were spiked either with ¹³³Ba or ²²⁶Ra and reacted under constant agitation during 120-406 days. The pH values ranged from 4 to 8 and solid to liquid (S/L) ratios varied from 0.01 to 5 g/l. The uptake of the radiotracers by barite was monitored through repeated sampling of the aqueous solutions and radiometric analysis. For both ¹³³Ba and ²²⁶Ra, our data consistently showed a continuous, slow decrease of radioactivity in the aqueous phase.Mass balance calculations indicated that the removal of ¹³³Ba activity from aqueous solution cannot be explained by surface adsorption only, as it largely exceeded the 100% monolayer coverage limit. This result was a strong argument in favor of recrystallization (driven by a dissolution-precipitation mechanism) as the main uptake mechanism. Because complete isotopic equilibration between aqueous solution and barite was approached or even reached in some experiments, we concluded that during the reaction all or substantial fractions of the initial solid had been replaced by newly formed barite.The ¹³³Ba data could be successfully fitted assuming constant recrystallization rates and homogeneous distribution of the tracer into the newly formed barite. An alternative model based on partial equilibrium of ¹³³Ba with the mineral surface (without internal isotopic equilibration of the solid) could not reproduce the measured activity data, unless multistage recrystallization kinetics was assumed. Calculated recrystallization rates in the salt solutions ranged from 2.8 × 10⁻¹¹ to 1.9 × 10⁻¹⁰ mol m⁻² s⁻¹ (2.4-16 μmol m⁻² d⁻¹), with no specific trend related to solution composition. For the suspensions prepared in pure water, significantly higher rates (∼5.7 × 10⁻¹⁰ mol m⁻² s⁻¹ or ∼49 μmol m⁻² d⁻¹) were determined.Radium uptake by barite was determined by monitoring the decrease of ²²⁶Ra activity in the aqueous solution with alpha spectrometry, after filtration of the suspensions and sintering. The evaluation of the Ra uptake experiments, in conjunction with the recrystallization data, consistently indicated formation of non-ideal solid solutions, with moderately high Margules parameters (W_AB = 3720-6200 J/mol, a₀ = 1.5-2.5). These parameters are significantly larger than an estimated value from the literature (W_AB = 1240 J/mol, a₀ = 0.5).In conclusion, our results confirm that radium forms solid solutions with barite at fast kinetic rates and in complete thermodynamic equilibrium with the aqueous solutions. Moreover, this study provides quantitative thermodynamic data that can be used for the calculation of radium concentration limits in environmentally relevant systems, such as radioactive waste repositories and uranium mill tailings.     

Growth of bultfonteinite and hydrogarnet in metasomatized basalt xenoliths in the B/K9 kimberlite, Damtshaa, Botswana: insights into hydrothermal metamorphism in kimberlite pipes

Metamorphic assemblages within Karoo basalt xenoliths, found within volcaniclastic kimberlite of the B/K9 pipe, Damtshaa, Botswana, constrain conditions of kimberlite alteration. Bultfonteinite and chlorite partially replace the original augite-plagioclase assemblage, driven by the serpentinisation of the kimberlite creating strong chemical potential gradients for Si and Mg. Hydrogarnet and serpentine replace these earlier metamorphic assemblages as the deposits cool. The bultfonteinite (ideally Ca₂SiO₂[OH,F]₄) and hydrogarnet assemblages require a water-rich fluid containing F⁻, and imply hydrothermal alteration dominated by external fluids rather than autometamorphism from deuteric fluids. Bultfonteinite and hydrogarnet are estimated to form at temperatures of ca. 350–250°C, which are similar to those for serpentinisation. Alteration within the B/K9 kimberlite predominantly occurs between 250 and 400°C. We attribute these conditions to increased efficiency of mass transfer and chemical reactions below the critical point of water and a consequence of volume-increasing serpentinisation and metasomatic reactions that take place over this temperature range. A comparison of the B/K9 kimberlite with kimberlites from Venetia, South Africa suggests that the composition and mineralogy of included xenoliths affects the alteration assemblages within kimberlite deposits.     

Selenium and other trace element in phosphorites: A comparison between those of the Bayovar-Sechura and other provenances

Data of trace element composition of phosphorites are scarce and incomplete. Phosphorites of different origins can vary substantially in trace element contents. In this paper 20 trace element concentrations of 35 sample phosphorites are reported. The geographical provenance is: Bayovar-Sechura (Peru), Khouribga, Youssoufia and Boucraa (Morocco), Gafsa (Tunisia), Florida (USA), Idaho and Phosphoria Formation (USA), North Carolina (USA), Algeria, Israel, Senegal, Syria and Togo. Aqua regia extracts were used to estimate the “pseudototal” values, following standard procedures (ISO 11466, 2002) and measured by ICP-AES and ICP-MS.     

Atlanta’s urban heat island under extreme heat conditions and potential mitigation strategies

The urban heat island (UHI), together with summertime heat waves, foster’s biophysical hazards such as heat stress, air pollution, and associated public health problems. Mitigation strategies such as increased vegetative cover and higher albedo surface materials have been proposed. Atlanta, Georgia, is often affected by extreme heat, and has recently been investigated to better understand its heat island and related weather modifications. The objectives of this research were to (1) characterize temporal variations in the magnitude of UHI around Metro Atlanta area, (2) identify climatological attributes of the UHI under extremely high temperature conditions during Atlanta’s summer (June, July, and August) period, and (3) conduct theoretical numerical simulations to quantify the first-order effects of proposed mitigation strategies. Over the period 1984–2007, the climatological mean UHI magnitude for Atlanta-Athens and Athens-Monticello was 1.31 and 1.71°C, respectively. There were statistically significant minimum temperature trends of 0.70°C per decade at Athens and −1.79°C per decade at Monticello while Atlanta’s minimum temperature remained unchanged. The largest (smallest) UHI magnitudes were in spring (summer) and may be coupled to cloud-radiative cycles. Heat waves in Atlanta occurred during 50% of the years spanning 1984–2007 and were exclusively summertime phenomena. The mean number of heat wave events in Atlanta during a given heat wave year was 1.83. On average, Atlanta heat waves lasted 14.18 days, although there was quite a bit of variability (standard deviation of 9.89). The mean maximum temperature during Atlanta’s heat waves was 35.85°C. The Atlanta-Athens UHI was not statistically larger during a heat wave although the Atlanta-Monticello UHI was. Model simulations captured daytime and nocturnal UHIs under heat wave conditions. Sensitivity results suggested that a 100% increase in Atlanta’s surface vegetation or a tripling of its albedo effectively reduced UHI surface temperature. However, from a mitigation and technological standpoint, there is low feasibility of tripling albedo in the foreseeable future. Increased vegetation seems to be a more likely choice for mitigating surface temperature.     

Geotechnical,Geological, and Hydrologic Characterization of a 52 km Electrical Power Transmission Line Alignment Route in Southeastern Nigeria

A 132 kVA electrical transmission line has been proposed to connect the towns of Eket and Ikot Abasi in the eastern Niger delta in Nigeria. A geotechnical and hydrological study was performed to geotechnically characterize the route alignment and to provide data for design of the foundations for the transmission towers. In this paper, we introduce the study location and its geological, topographical and physiological characteristics, present the hydrological and geotechnical investigations and their results, and make recomendations for the design of the transmission tower foundations. Hydrological inspection of the power line alignment revealed that the route is traversed by numerous tributaries of the Qua-Iboe and Imo Rivers, the two major rivers that control the drainage of the study area. In-situ geotechnical tests consisted of cone penetration tests (CPTs), vane shear tests, test pit sampling (0–2.0 m depth) and lithologic boreholes (20 and 50 m deep). Laboratory tests included grain size analysis, pH determination and Atterberg Limits. Based on the CPT log pattern, no of stratum, and refusal depths, the soils along the transmission alignment were classified into twelve structural domains having common geotechnical properties. Because of the elevated water levels, and the nature of the soils, deep pile foundations were recommended for the towers. Software from the Louisiana Transportation Research Center, was employed to estimate skin friction, end bearing, and ultimate bearing capacities for assumed 225 mm square shaped reinforced concrete pile in each of the different zones of the alignment.     

A 44-year high-resolution ocean and atmospheric hindcast for the Mediterranean Basin developed within the HIPOCAS Project

A set of 44-year (1958–2001) homogeneous and high-resolution hindcasts of atmospheric, sea level residuals, and wave states was performed for the Mediterranean Basin within the framework of the HIPOCAS European Project. To this aim, different numerical models were used. As a first step, a Mediterranean high-resolution atmospheric database, suitable to provide realistic and homogeneous forcing for ocean hindcast runs was generated. The HIPOCAS atmospheric database was created by means of dynamical downscaling from the global reanalysis NCEP, using for that the limited area model SN-REMO along with a spectral nudging technique. In a second stage, different Mediterranean oceanic hindcasts were performed. On one hand a long-term database of sea state over the western Mediterranean was generated by means of the wave model WAM and on the other hand a sea level residual database containing storm surge events was obtained from a long-term integration of the HAMSOM model over the entire basin. The three different hindcast runs have been exhaustively validated. On that score, various simulated parameters have been compared to both satellite and in situ measurements. Such comparisons provide a measure of the skills of the different simulated fields to realistically reproduce the observed features. Once these skills are evaluated, a study of the ocean and atmospheric climate trends as well as the interannual variability for the whole 44-year period was carried out with the hindcasted data. The reliability of the data as shown by its comparison to measurements and a proven temporal homogeneity over the 44 years of simulation make the Mediterranean HIPOCAS ocean–atmosphere hindcasted database a useful tool for studies focused on regional climatic variability, as well as for further applications in coastal and environmental decision processes in the Mediterranean area.     

Mechanisms of expansion for an introduced species of cordgrass, Spartina densiflora, in Humboldt Bay, California

The dominant plant in Humboldt Bay salt marshes in Spartina densiflora, a species of cordgrass apparently introduced from South America. At several salt marshes and restoration sites around Humboldt Bay, distribution of this plant has increased significantly. We investigated the relative contributions of vegetative tiller production and seed germination to the establishment and expansion of S. densiflora. Lateral spread of plants surrounded by competitors were compared to areas without competing plant species. Plants growing in areas without competitors had significantly higher rates of vegetative expansion (p<0.0001). Viable seed production, germination rates, seedling survivorship, and growth of adult plants were measured in six salinity treatments. Approximately 1,977±80 viable seeds are produced per plant (0.25–0.5 m²). The number of germinating seeds was inversely related to increases in salinity. Salinity treatments between 19‰ and 35‰ produced significantly lower germination rates than salinities of 0–18‰ (p<0.0001). Seedling survivorship was 50% at ≤4‰ and 8–14% at ≥11‰. Lateral expansion of adult, greenhouse-grown plants occurred in all salinity treatments, with modest decreases in the highest salinity treatments (p<0.05). Our findings indicate that S. densiflora expands primarily by vegetative expansion, and lateral tillers are produced by throughout the year. Spartina densiflora produces prolific amounts of seed, but recruitment in mature salt marshes may be limited by competitors and higher salinities. At restoration sites, planting of native species such as Salicornia virginica, Distichlis spicata, or Jaumea carnosa may prevent monospecific stands of S. densiflora from developing.