Ecological quality assessment of small estuaries from the Portuguese coast based on benthic macroinvertebrate assemblages indices

Benthic macroinvertebrates communities are the most consistently emphasized biotic component of aquatic ecosystems and are one of the biological indicators required for assessment by the European Water Framework Directive. In this context, several indices based on these communities have been developed in order to assess ecological quality of estuarine systems. In the present work we used AMBI, M-AMBI, BENTIX and BAT to distinguish ecological status of five small estuarine systems of the Portuguese south and southwest coasts. Although indices outputs did not differ between systems and sampling seasons, results indicated that the metrics in which these indices are based could differentiate community structures as a result of two main gradients that force these communities: the natural variability, and the anthropogenic impact.     

System parameters of soil foundations for time domain dynamic analysis

Soil-structure interaction analysis is usually carried out in the frequency domain, because the compliance functions of the half-space are known only in the frequency domain. Since non-linear analysis cannot be carried out in the frequency domain, a system with frequency independent parameters is used to represent the half-space soil medium so that a nonlinear analysis in the time domain becomes possible. The objective of this paper is to propose a system with lumped parameters, which are independent of frequency, to represent the half-space soil medium. The proposed frequency independent system consists of a number of real discrete structure elements; thus the existing dynamic analysis programs may be adoptable with little modification. In this paper, the parameters are found by minimizing the sum of the squares of deviations between the steady-state responses of the theoretical half-space model and those of the lumped parameter system over a specified frequency range. Once the parameters have been found, the lumped parameter system can be used in practical applications for time domain dynamic analysis of either linear or non-linear structures. In comparison with the dynamic response of the theoretical half-space model, the lumped parameter system yields satisfactory results.     

Determination of Rare Earth Elements, Sc, Y, Zr, Ba, Hf and Th in Geological Samples by ICP-MS after Tm Addition and Alkaline Fusion

We present a revised method for the determination of concentrations of rare earth (REE) and other trace elements (Y, Sc, Zr, Ba, Hf, Th) in geological samples. Our analytical procedure involves sample digestion using alkaline fusion (NaOH-Na₂O₂) after addition of a Tm spike, co-precipitation on iron hydroxides, and measurement by sector field-inductively coupled plasma-mass spectrometry (SF-ICP-MS). The procedure was tested successfully for various rock types (i.e., basalt, ultramafic rock, sediment, soil, granite), including rocks with low trace element abundances (sub ng g⁻¹). Results obtained for a series of nine geological reference materials (BIR-1, BCR-2, UB-N, JP-1, AC-E, MA-N, MAG-1, GSMS-2, GSS-4) are in reasonable agreement with published working values.     

A densification mechanism to model the mechanical effect of methane hydrates in sandy sediments

Recent pore-scale observations and geomechanical investigations suggest the lack of true cohesion in methane hydrate-bearing sediments (MHBSs) and propose that their mechanical behavior is governed by kinematic constrictions at pore-scale. This paper presents a constitutive model for MHBS, which does not rely on physical bonding between hydrate crystals and sediment grains but on the densification effect that pore invasion with hydrate has on the sediment mechanical properties. The Hydrate-CASM extends the critical state model Clay and Sand Model (CASM) by implementing the subloading surface model and introducing the densification mechanism. The model suggests that the decrease of the sediment available void volume during hydrate formation stiffens its structure and has a similar mechanical effect as the increase of sediment density. In particular, the model attributes stress-strain changes observed in MHBS to the variations in sediment available void volume with hydrate saturation and its consequent effect on isotropic yield stress and swelling line slope. The model performance is examined against published experimental data from drained triaxial tests performed at different confining stress and with distinct hydrate saturation and morphology. Overall, the simulations capture the influence of hydrate saturation in both the magnitude and trend of the stiffness, shear strength, and volumetric response of synthetic MHBS. The results are validated against those obtained from previous mechanical models for MHBS that examine the same experimental data. The Hydrate-CASM performs similarly to previous models, but its formulation only requires one hydrate-related empirical parameter to express changes in the sediment elastic stiffness with hydrate saturation.     

Performance of the Nuclear Compton Telescope

On 1 June 2005, the prototype Nuclear Compton Telescope (NCT) flew on a high altitude balloon from Fort Sumner, New Mexico. NCT is a balloon-borne soft γ-ray (0.2–10 MeV) telescope for studying astrophysical sources of nuclear line emission and γ-ray polarization. Our program is designed to develop and test technologies and analysis techniques crucial for the Advanced Compton Telescope; however, our detector design and configuration is also well matched to the focal plane requirements for focusing Laue lenses. The NCT prototype utilizes two, 3D imaging germanium detectors (GeDs) in a novel, ultra-compact design optimized for nuclear line emission in the 0.5–2 MeV range. Our prototype flight provides a critical test of the novel detector technologies, analysis techniques, and background rejection procedures developed for high resolution Compton telescopes.     

Likelihood analysis of repeating in the BATSE catalogue

I describe a new likelihood technique, based on counts-in-cells statistics, that I use to analyze repeating in the BATSE 1B and 2B catalogues. Using the 1B data, I find that repeating is preferred over non-repeating by 4.3:1 odds, with a peak at 5–6 repetitions per source. I find that the post-1B data are consistent with the repeating model inferred from the 1B data, after taking into account the lower fraction of bursts with well-determined positions. Combining the two data sets, I find that the odds favoring repeating over non-repeating are almost unaffected at 4:1, with a narrower peak at 5 repetitions per source. I conclude that the data sets are consistent both with each other and with repeating, and that for these data sets the odds favor repeating. Compton GRO Fellow - NASA grant GRO/PDP 93-08.     

Sulfide mineralogy and redox conditions in some shergottites

Abstract— Magmatic sulfide mineralogy has been studied in 2 olivine‐phyric shergottites (DaG 476 and SaU 005) and 4 basaltic shergottites (Zagami, Shergotty, Los Angeles, and NWA 480). Modal abundances of magmatic sulfides, as estimated by image analysis on thin section, are high (0.16 to 0.53 area percent) and correlate positively with abundances of Fe‐Ti oxides. Sulfides are mesostasis minerals, being mostly interstitial grains or locally enclosed in post‐cumulus melt inclusions (e.g., SaU 005) in olivine. Sulfides in shergottites are composed of major pyrrhotite containing pentlandite exsolutions associated with minor amounts of Cu sulfides (chalcopyrite and/or cubanite). Hot desert finds (e.g., DaG 476) show abundant fracture‐filling iron (oxy)hydroxides of probable terrestrial origin. Unaltered sulfides show metal‐rich hexagonal pyrrhotite compositions with metal/sulfur (M/S) ratio ranging between 0.936 ± 0.005 and 0.962 ± 0.01. This compositional range corresponds to the two‐phase structural domain 2C + nC of the Fe‐S system; however, the high‐temperature disordered hexagonal 1C pyrrhotite structure would be in better agreement with magnetic properties of shergottites. Ni contents in pyrrhotite increase from Los Angeles (<0.05 at%) to Shergotty, Zagami, and NWA 480 (0.2–0.5 at%), and DaG 476 and SaU 005 (up to 3 at%). The higher Ni values of pyrrhotite in olivine‐phyric shergottites correlate with the abundance of pentlandite exsolutions, both reflecting more primitive Ni‐rich sulfide liquids where abundant olivine crystallized. This result and the strong correlation between sulfide abundances and Fe‐Ti oxides argue for a primary magmatic origin of these sulfides. Although they reproduce the trend of magmatic oxygen fugacity conditions determined from Fe‐Ti oxide pairs, observed pyrrhotite compositions are systematically more metal‐deficient compared to those calculated from the Fe‐S‐O system. This suggests post‐magmatic oxidation during cooling on Mars, followed by terrestrial weathering for hot desert finds.     

Effective stress analysis of seismic site response

A procedure is presented which allows site response analyses to be performed with any general multidimensional finite element analysis package. Numerical results which corrorate the theory are presented. Also, as an illustration of the procedure, results of an effective stress analysis for the scismic response and liquefaction of a horizontally layered saturated sand deposit are presented.     

F. E. analysis of field consolidation curves obtained with the modified borehole shear device (BHSD)

A modified version of the bore hole sheat device (BHSD) was used to obtain field consolidation curves in a soft sensitive clay. The Porewater pressure dissipation was monitored at the centre of one of the shear plates. This paper describes briefly the in situ device employed and demonstrates the basic features of the linearelastic F. E. program ‘SOL’. A detailed study is made to simulate the field behaviour with the finite element approach. Comparisons are made between the field and analytical consolidation behaviour. Difficulties in predicting the value of the coefficient of consolidation of a sensitive clay using the BHSD consolidation curves are discussed.