Non-linear hydrodynamical evolution of rotating relativistic stars: numerical methods and code tests

We present numerical hydrodynamical evolutions of rapidly rotating relativistic stars, using an axisymmetric, non-linear relativistic hydrodynamics code. We use four different high-resolution shock-capturing (HRSC) finite-difference schemes (based on approximate Riemann solvers) and compare their accuracy in preserving uniformly rotating stationary initial configurations in long-term evolutions. Among these four schemes, we find that the third-order piecewise parabolic method scheme is superior in maintaining the initial rotation law in long-term evolutions, especially near the surface of the star. It is further shown that HRSC schemes are suitable for the evolution of perturbed neutron stars and for the accurate identification (via Fourier transforms) of normal modes of oscillation. This is demonstrated for radial and quadrupolar pulsations in the non-rotating limit, where we find good agreement with frequencies obtained with a linear perturbation code. The code can be used for studying small-amplitude or non-linear pulsations of differentially rotating neutron stars, while our present results serve as testbed computations for three-dimensional general-relativistic evolution codes.     

Symbiodinium (internal transcribed spacer 2) diversity in the coral host Agaricia lamarcki (Cnidaria: Scleractinia) between shallow and mesophotic reefs in the Northern Caribbean (20–70 m)

This study investigated differences in Symbiodinium diversity in the scleractinian coral species Agaricia lamarcki between shallow (20–25 m) and mesophotic (50–70 m) depths in the Northern Caribbean. Corals were sampled in each of four shallow sites (20–25 m; n = 18) and three mesophotic sites (50–70 m; n = 18) from Mona Island (Puerto Rico) and the US Virgin Islands during a mesophotic exploratory cruise and from the La Parguera shelf edge, off Southwestern Puerto Rico. Symbiodinium diversity was assessed using internal transcribed spacer 2 sequences clustered into operational taxonomic units (OTUs). Clustering resulted in eight clade C OTUs and one clade D OTU. Of these, there were three common Symbiodinium OTUs consisting of C3 and D1a.N14 in shallow reefs and C11.N4 in mesophotic reefs. Statistical tests (permutational multivariate analysis of variance and analysis of similarity) showed significant differences between clade C Symbiodinium OTUs in A. lamarcki colonies located at shallow and mesophotic depths, indicating symbiont zonation. Symbiodinium diversity in A. lamarcki from the Northern Caribbean is comparable to previous reports in the Southern Caribbean for this species. This is the first report of the thermal tolerant species Symbiodinium trenchii (D1a) in A. lamarcki.     

Eiefsis Bay Anoxia: Nutrient Conditions and Benthic Community Structure

Abstract. The changes in the concentrations of silicate, phosphate, and inorganic nitrogen in Eiefsis Bay. an intermittently anoxic basin, arc described and related to the changes in the physical properties of the water. Winter convection resulted in a very small vertical gradient of temperature, salinity, oxygen, and nutrients. Stratification started to develop in May and persisted for about 6 months. High values of silicate, phosphate, and ammonia occurred during the anoxic conditions prevailing in summer. The vertical transport of particulate organic matter and decomposition of abundant pelagic and benthic organic matter during the summer produced a low oxygen level in the bottom layer below the pycnoclinc. A high sea water temperature and vertical stability contributed to the development of anoxic conditions during the summer in the near bottom layer and to mass mortality of benthic macrofauna. Also the Eiefsis Bay anoxia appears to have had significant ecological effects on many other marine species, including several of economic importance.     

Turnover time of waters in a deep basin in the Aegean Sea

The Western Gulf is a basin in the Saronikos Gulf. Below about 100 m the water is almost stagnant, essentially isothermal (around 14°C) and it has practically uniform salinity. The level and the mechanism of enrichment in nutrients is discussed. The age of the water estimated from nutrient budget calculations is between one and eight years. The replacement time of water is similar to that found in the Santa Barbara basin, but different from those of the Cariaco Trench and the Black Sea.     

A Comparison Between Modelled and Measured Mixing-Layer Height Over Munich

An attempt is made to correlate the mixing heights, derived from ceilometer and Sodar measurements, to those simulated by different atmospheric boundary-layer parameterization schemes. The comparison is performed at two sites (one suburban and one rural) close to Munich, Germany for two spring and two winter days. It is found that, under convective conditions, the mixing height determined, by both Sodar and ceilometer, corresponds to the middle or the top of the entrainment zone, respectively, as calculated from the eddy-viscosity profiles. Under stable conditions, the measured mixing height is related to the height where eddy viscosities attain their minimum values (Sodar) or to the height of residual mechanical turbulence (ceilometer). During a foehn case with weak turbulence, the measured mixing height from both Sodar and ceilometer is better inferred by considering the eddy-viscosity profiles during daytime and the height of the low-level jet during nighttime.     

Geometry of trapezoidal fan deltas and their relationship to extensional faulting along the southwestern active margins of the Corinth rift, Greece

A new subtype of Gilbert-type fan deltas, ‘the trapezoidal fan delta’, characterized by the absence of bottomset deposits, is recognized in the south-western active margins of the Corinth rift in central Greece. They are formed adjacent to master extensional listric faults and developed by progradation either onto a subaqueous basin escarpment or across a subaerial platform where alluvial fans have accumulated. Simultaneously with master fault activity, displacements on counter faults along intrabasinal basement highs produced fan delta foreset deposits. Furthermore, footwall imbrication and uplift along the listric faults, as well as transfer fault displacement, have strongly influenced the pattern of fan delta sedimentation.     

Effects of climatic variability on the hydrologic response of a freshwater watershed

A generalized watershed model was used to evaluate the effects of global climate changes on the hydrologic responses of freshwater ecosystems. The Enhanced Trickle Down (ETD) model was applied to W-3 watershed located near Danville, Vermont. Eight years of field data was used to perform model calibration and verification and the results were presented in Nikolaidis et al., (1993). Results from the Goddard Institute for Space Studies (GISS) and the Geophysical Fluid Dynamics Laboratory (GFDL) general circulation models which simulated the doubling of present day atmospheric CO₂ scenarios were used to perform the hydrologic simulations for the W-3 watershed. The results indicate that the W-3 watershed will experience increases in annual evapotranspiration and decreases in annual outflow and soil moisture. Stochastic models that simulate collective statistical properties of meteorological time series were developed to generate data to drive the ETD model in a Monte-Carlo fashion for quantification of the uncertainty in the model predictions due to input time series. This coupled deterministic and stochastic model was used to generate probable scenarios of future hydrology of the W-3 watershed. The predicted evapotranspiration and soil moisture under doubling present day atmospheric CO₂ scenarios exceed the present day uncertainty due to input time series by a factor greater than 2. The results indicate that the hydrologic response of the W-3 watershed will be significantly different than its present day response. The Enhanced Trickle Down model can be used to evaluate land surface feedbacks and assessing water quantity management in the event of climate change.     

Evaluation of Batch Leaching Procedures for Estimating Metal Mobility in Glaciated Soils

Batch leaching methods have been used for several decades to estimate the potential release of contaminants from soils. Four batch leaching procedures (toxicity characteristic leaching procedure, synthetic precitation leaching procedure, deionized water leaching procedure, and California waste extraction test) were evaluated for their ability to realistically quantify the mobility of metals from previously contaminated glaciated soils. The study was conducted using soils from four different sites (three in Connecticut and one in Maine). The results of the batch leaching procedures were compared with a set of continuous column leaching experiments performed at two different flowrates and two influent pH values. The results suggested that the synthetic precipitation leaching procedure (SPLP) was more realistic than the toxicity characteristic leaching procedure (TCLP), but still a conservative leaching estimate for evaluating the potential for metal mobility in glaciated soils. This study suggests that using SPLP as a test for estimating metal cleanup levels will result in lower remediation costs relative to TCLP or waste extraction test (WET), but still maintain a high level of confidence in the protection of ground water quality.