Calorimetric study of the coesite-stishovite transformation and calculation of the phase boundary

High temperature drop-solution calorimetry in molten 2 PbO · B₂O₃ at 1044 K for coesite and stishovite polymorphs of silica was carried out to determine the enthalpy of the coesite-stishovite transition. These experiments were performed on high-purity, single-phase samples of coesite and stishovite. Our new value for the enthalpy of the coesitestishovite transition (ΔH ₂₉₈ ⁰ ) is 29.85 ± 0.78 kJ/mol, which is about 35% lower than previously reported by Akaogi and Navrotsky (1984) and Holm et al. (1967), but which compares well with new measurements by Akaogi et al. (1994b). Using these new data, we have calculated the equilibrium phase boundary between coesite and stishovite and obtained a slope, dP/dT=0.0031 (2) GPa/K. This calculated slope is in good agreement with that determined [0.0026 (2) GPa/K] from the in-situ X-ray diffraction study of Zhang et al. (1996).     

Progress and new directions in high temperature calorimetry revisited

 High temperature reaction calorimetry has seen considerable advances over the past twenty years. New and more sensitive calorimeters, improved sample handling techniques, and better control of the final dissolved state has made solution calorimetry and drop solution calorimetry, using molten lead borate and other solvents, very versatile and reliable techniques. This paper summarizes these advances and presents examples of specific applications to problems of transition metal oxide chemistry, high pressure geophysics, melt and glass energetics, and metastable materials relevant to the earth sciences. Received June 3, 1996 / Revised, accepted Spetember 23, 1996     

U-Th dating of Lake Lisan (late Pleistocene dead sea) aragonite and implications for glacial east Mediterranean climate change

U-series dating can be an effective means to obtain accurate and precise ages on Quaternary carbonates. However, most samples require a correction for U and Th in admixed detritus. This complication is often addressed through generation of U-Th isochrons, requiring analyses of several coeval samples. In addition, presence of water-derived (hydrogenous) Th in the carbonate can cause inaccuracies in isochron ages.This study reports a high-resolution U-series chronology of sediments deposited by Lake Lisan, the last glacial precursor of the Dead Sea. The strategy employed combines multiple measurements from a few stratigraphic heights and fewer analyses from many heights in a single described and measured section. The resulting chronology is based on ages at 22 heights in a ∼40-m-thick section covering the interval of ∼70-14 calendar ka BP. The effects of admixed detritus are evaluated using trace elements. Nearly pure aragonite samples, indicated by very low abundances of insoluble elements such as Nb and Zr, were found to contain hydrogenous Th, which causes the uncorrected U-²³⁰Th age of a modern sample to be ∼2.5 ka. Nevertheless, accurate ages have been obtained by correcting for the detrital and aqueous interferences. The resulting ages are in stratigraphic order, and their accuracy is evidenced by consistency of Lisan Formation U-series and ¹⁴C ages with the coral-based calendar-radiocarbon age calibration.The U-Th ages provide a context to unravel the limnological history of Lake Lisan. Boundaries between the Lower, Middle, and Upper stratigraphic units correspond to the MIS 4/3 and 3/2 transitions, respectively. During MIS 2 and 4 the lake generally showed a stable two-layer configuration and a positive fresh-water balance, reflected by deposition of laminated aragonite-detritus. Dry intervals during MIS 2 and 4 are indicated by thick gypsum layers and an inferred depositional hiatus, which are temporally associated with Heinrich events H1 at ∼17 ka and H6 at ∼65 ka, respectively. During MIS 3 the lake level was unstable with intermittent dry periods indicated by abundant clastic layers and a significant hiatus between ∼43-49 ka. Clastic layers are associated with Dansgaard-Oeschger events during MIS 3, and indicate lake level declines during abrupt Northern Hemisphere warmings. Overall, the climate of the Eastern Mediterranean region shows a strong linkage to the Northern Hemisphere climate, with increasing lake size and stability during cold periods, and fluctuations and dessication during warmings and Heinrich events.     

Electrodialytic remediation of CCA-treated waste wood in pilot scale

When chromated copper arsenate (CCA)-treated wood is removed from service and turns into waste, the contents of Cu, Cr and As remain high due to the strong fixation of CCA in the wood. This high content of toxic compounds presents a disposal challenge. Incineration of CCA-treated waste wood is not allowed in Denmark; instead, the wood is to be land-filled until new methods for handling the wood are available. Since the amounts of CCA-treated wood being removed from service is expected to increase in the years to come, the need for finding alternative handling methods is very relevant. In this study, the usefulness of Electrodialytic Remediation was demonstrated for handling of CCA-treated waste wood in pilot scale. The electrodialytic remediation method, which uses a low-level direct current (DC) as the cleaning agent, combines electrokinetic movement of ions in the wood matrix with the principles of electrodialysis. It has previously been shown that it is possible to remove Cu, Cr and As from CCA-treated wood using electrodialytic remediation in laboratory scale, but until now, the method had not been studied in large scale. The pilot-scale plant used in this study was designed to contain up to 2 m³ wood chips. Six remediation experiments were carried out. In these experiments, the process was up-scaled stepwise by increasing the distance between the electrodes from initially 60 cm to finally 150 cm. The remediation time was varied between 11 and 21 days, and phosphoric acid and/or oxalic acid was used to facilitate the desorption of CCA from the wood. In the most successful of the experiments carried out, the concentration of CCA in the wood was reduced by up to 82% for Cr, 88% for Cu and at least 96% for As.     

Case study on the strategy and application of enhancement solutions to improve remediation of soils contaminated with Cu, Pb and Zn by means of electrodialysis

Numerous studies have been conducted with electrochemical removal of heavy metals from spiked kaolinite. Meanwhile, when moving from kaolinite to real soils, new factors must be taken into account—factors influencing, e.g., the buffering capacity of the soil against acidification and the adsorption/desorption processes of the heavy metals. The present study gives some examples where it is necessary to use an enhancement solution to aid desorption of Cu, Zn and Pb during electrodialytic treatment. Dependent on the composition of the pollution, different choices can be made. In the case of a Cu-polluted calcareous soil, ammonia may be used as enhancement solution, due to the formation of charged complexes between ammonia and Cu. Thus, Cu is mobile at high pH when ammonia is added and Cu can be removed without dissolving the calcareous parts. Zn is also mobilized by ammonia, but to a lesser extent than Cu. In the case of Cu, Zn and Pb at the same time, alkaline ammonium citrate may be a solution. It was shown that this enhancement solution could mobilize these three pollutants, but optimization of concentration and pH of the ammonium citrate is still needed. When choosing a remediation scheme for electrochemical treatment of an actual industrially polluted soil, this scheme must be chosen on basis of characterization of soil and pollution combination.     

Energetics of radiation damage in natural zircon (ZrSiO4)

Transposed temperature drop calorimetry at 1000 °C was performed on natural zircons (ZrSiO₄) from Sri Lanka that were partially to completely metamict due to α-decay event damage (0.06 to 11.7×10¹⁵ α-decay events/mg). The enthalpy of annealing at room temperature (ΔH_anneal) varies sigmoidally as a function of radiation dose. ΔH_anneal reaches a saturation plateau at radiation doses greater than 5×10¹⁵ α-decay events/mg. The annealing of several samples to a crystalline structure with broadened diffraction peaks does not significantly affect the enthalpy of annealing. The large magnitude of the enthalpy of annealing plateau, ?59±3 kJ/mol, suggests that the damage to the structure is pervasive on the scale of Angstroms, consistent with the loss of mid-range order characteristic of a glass. The energetics are consistent with, but do not require, chemical heterogeneity caused by micro-domains of amorphous SiO₂-rich and ZrO₂-rich regions in the metamict state.     

New variable stars from the photographic archive: semi-automated discoveries,attempts at automatic classification and the new field 104 Her

Using 172 plates taken with the 40-cm astrograph of the Sternberg Astronomical Institute(Lomonosov Moscow University) in 1976–1994 and digitized with a resolution of 2400 dpi, we discovered and studied 275 new variable stars. We present the list of our new variables with all necessary information concerning their brightness variations. As in our earlier studies, the new discoveries show a rather large number of high-amplitude Delta Scuti variables, predicting that many stars of this type remain not detected in the whole sky. We also performed automated classification of the newly discovered variable stars based on the Random Forest algorithm. The results of the automated classification were compared to traditional classification and showed that automated classification was possible even with noisy photographic data. However, further improvement of automated techniques is needed, which is especially important when considering the very large numbers of new discoveries expected from all-sky surveys.     

High levels of site fidelity in movement patterns of Southern Rock Lobster (Jasus edwardsii) in Victoria,Australia

ABSTRACT

Movement patterns of the Southern Rock Lobster Jasus edwardsii in Victoria, Australia were investigated from 8,533 tag-recapture events across a 20-year period (1992–2012). In total, 83% of lobsters were recaptured within 1?km of their tagging site and 93% within 5?km. While largely resident, elevated movements were observed within specific regions, with the overall direction of movement being from inshore to offshore areas. Movement was not impacted by lobster sex, size, or reproductive stage. The fishery for Southern Rock Lobster within Victoria is currently managed into two zones with separate total allowable commercial catches in each area. Given the high levels of site fidelity, our findings suggest that management of the resource at this spatial scale is appropriate and that consideration of significant movement between zones is not warranted in fishery stock assessment models.     

Variation among fossil chironomid assemblages in surficial sediments of Bodensee-Untersee (SW-Germany): implications for paleolimnological interpretation

In paleolimnology, subfossil head capsules of chironomids play an important role as ecological indicators of lake history. It is important to determine, therefore, whether fossil assemblages are representative of former biocoenoses. There is evidence that headcapsules washed in from other places can make up a significant percentage of the total. As interpretations are usually drawn from the examination of a single core, it is of special interest to know whether a fossil assemblage of a single site properly reflects limnological conditions of the whole lake. This study examined the taxonomic distribution of subfossil chironomids in the surficial sediments of the Bodensee-Untersee, with the aim of assessing the variability in chironomid assemblages. Apparently, most of the head capsules of the profundal fossil assemblages in the Untersee had been washed in from the littoral zone or from the slope. Although the Bodensee-Untersee is a rather large lake, variability is surprisingly low among all samples. Therefore a correct interpretation from a single core may be possible.