Nature of polymerization and properties of silicate melts and glasses at high pressure

The structures of sodium silicate and aluminosilicate glasses quenched from melts at high pressure (6-10 GPa) with varying degrees of polymerization (fractions of nonbridging oxygen) were explored using solid-state NMR [¹⁷O and ²⁷Al triple-quantum magic-angle spinning (3QMAS) NMR]. The bond connectivity in melts among four and highly coordinated network polyhedra, such as ^[4]Al, ^[5,6]Al, ^[4]Si, and ^[5,6]Si, at high pressure is shown to be significantly different from that at ambient pressure. In particular, in the silicate and aluminosilicate melts, the proportion of nonbridging oxygen (NBO) generally decreases with increasing pressure, leading to the formation of new oxygen clusters that include 5- and 6-coordinated Si and Al in addition to 4-coordinated Al and Si, such as ^[4]Si-O-^[5,6]Si, ^[4]Si-O-^[5,6]Al and Na-O-^[5,6]Si. While the fractions of ^[5,6]Al increase with pressure, the magnitude of this increase diminishes with increasing degrees of ambient-pressure polymerization under isobaric conditions. Incorporating the above structural information into models of melt properties reproduces the anomalous pressure-dependence of O²⁻ diffusivity and viscosity often observed in silicate melts.     

Iron and Sulfur Chemistry in a Stratified Lake: Evidence for Iron-Rich Sulfide Complexes

A four month study of a man-made lake used for hydroelectric power generation in northeastern Pennsylvania USA was conducted to investigate seasonal anoxia and the effects of sulfide species being transported downstream of the power generation equipment. Water column analyses show that the system is iron-rich compared to sulfide. Total Fe(II) concentrations in the hypolimnion are typically at least twice the total sulfide levels. In situ voltammetric analyses show that free Fe(II) as [Fe(H₂O)₆]²⁺ or free H₂S as H₂S/HS^- are either not present or at trace levels and that iron-rich sulfide complexes are present. From the in situ data and total Fe(II) and H₂S measurements, we infer that these iron-rich sulfide complexes may have stoichiometries such as Fe₂SH³⁺ (or polymeric forms of this and other stoichiometries). These iron-rich sulfide complexes appear related to dissolution of the iron-rich FeS mineral, mackinawite, because IAP calculations on data from discrete bottle samples obtained from bottom waters are similar to the pK_sp of mackinawite. Soluble iron-sulfide species are stable in the absence of O₂ (both in lake waters and the pipeline) and transported several miles during power generation. However, iron-sulfide complexes can react with O₂ to oxidize sulfide and can also dissociate releasing volatile H₂S when the waters containing them are exposed to the atmosphere downstream of the powerplant. Sediment analyses show that the lake is rich in oxidized iron solids (both crystalline and amorphous). Fe concentrations in FeS solids are low (<5 μmole/gr_{dry wt}) and the pyrite concentration ranges from about equal to the solid FeS to 30 times the solid FeS concentration. The degree of pyritization is below 0.12 indicating that pyrite formation is limited by free sulfide, which can react with the iron-rich sulfide complexes.     

FT-IR Spectroscopic Investigation of Hydrous Components in Sillimanite from Eastern Ghat Granulite Belt, India

FT-IR spectra of sillimanite samples from high grade regionally metamorphosed rocks belonging to the granulite terrain (amphibolite to pyroxene granulite facies) deciphers prominent OH features. Heating experiments indicate growth of prominent band at 3161cm⁻¹. Heating above 1000°C all OH features disappear in intensity into broad features with slight shift of bands towards lower energies. Complete dehydration requires temperatures above 1000°C. Coexistence of boron and OH features are also observed in all sillimanite samples. The high temperature behaviour of sillimanite from the granulite terrain discerns that the hydrous species in sillimanite were incorporated much below 700°C, however, secondary hydration due to pegmatite activity, retrograde metamorphism and migmatisation is not ruled out. Thus a near anhydrous condition were probably not achieved during the granulite facies metamorphism in Eastern ghat granulite terrain.     

A Preliminary Survey of the Level of Microbiological Pollution of Major Rivers in Northern Greece

The objective of the present survey was to assess the microbiological quality of river waters used mainly to irrigate the large plains of Macedonia and Thessaly in Northern Greece. Five rivers (Aliakmonas, Axios, Loudias, Mavroneri and Pineios) were sampled during a 10‐month period (June 2002 – March 2003) for Total Microbial Flora (TMF) at 22 °C and 37 °C, Total Coliforms (TC), Fecal Coliforms (FC), enterococci, staphylococci, Pseudomonas, fungi, Giardia spp. and Cryptosporidium spp. The results indicate moderate to high microbiological pollution, with the highest levels of microbial pollution found in Mavroneri and Pineios Rivers, and moderate pollution levels in Aliakmonas, Axios and Loudias Rivers. The extent of microbiological pollution is accentuated by the fact that Giardia‐ and/or Cryptosporidium cysts were detected in nine out of eleven samples collected in June 2002 with excessive Giardia counts demonstrated for Pineios River. The microbiological pollution of the surveyed rivers is attributed to various degrees of human interference and to lack of ample pollution monitoring systems, which emphasize the need for implementation of the EU Water Framework Directive.     

On a modal damping identification model for non-classically damped linear building structures subjected to earthquakes

A simple modal damping identification model developed by the present authors for classically damped linear building frames is extended here to the non-classically damped case. The modal damping values are obtained with the aid of the frequency domain modulus of the roof-to-basement transfer function and the resonant frequencies of the structure (peaks of the transfer function) as well as the modal participation factors and mode shapes of the undamped structure. The assumption is made that the modulus of the transfer function of the non-classically damped structure matches the one of the classically damped structure in a discrete manner, i.e., at the resonant frequencies of that function modulus. This proposed approximate identification method is applied to a number of plane building frames with and without pronounced non-classical damping under different with respect to their frequency content earthquakes and its limitations and range of applicability are assessed with respect to the accuracy of both the identified damping ratios and that of the seismic structural response obtained by classical mode superposition and use of those identified modal damping ratios.     

北喀斯喀特边缘IODP 311航次断面的地震结构、天然气水合物含量和滑塌构造

北喀斯喀特活动边缘的增生楔沉积物中含有分布广泛的天然气水合物一直延伸到海底下几百米的深度。为了评估天然气水合物的长期能源潜力和它在全球气候变化及边坡稳定性中的作用,2005年9月IODP311航次建立了一个详细的地质模型来解释水合物的形成与分解以及它与穿过大陆边缘流体流的伴生关系。在考察前,先在大陆坡上进行地震试验以提供支持钻井的地球物理信息。     

Effects of rotation on the colours and line indices of stars 5. The ZRMS and the ZRZAMS

The observeduvby and H_α indices of member stars of the Hyades and Praesepe clusters have been analysed in detail for rotation effects. The Alpha Persei, Pleiades and the Centaurus subgroup of the Scorpio—Centaurus association have been reanalysed using the observed indices instead of the extinction-corrected indices used earlier. The observed rotation effects from the analysis of these cluster data are found to be in excellent agreement with the theoretical predictions of Collins & Sonneborn (1977). We have also analysed the α,c and (u − b) values of the member stars of NGC 1976, 2264, 2287, 2422, 4755,1C 2391, IC 2602 and IC 4665 for rotation effects. The results are found to be consistent with the theoretical predictions. The observed slopes of the rotation effects were used to determine the zero rotation main sequence values of the intermediate band photometric indices for selected clusters. We also corrected the observed indices for each star in each cluster using the theoretical predictions of Collins and Sonneborn and derived the ZRMS values for each cluster. The agreement between the two determinations is found to be good. The various ZRMS curves were utilised to derive the ZRZAMS values. A preliminary calibration of the absolute visual magnitudes as a function of α valid for ZRZAMS has also been derived. The ZRMS values of the intermediate band photometric indices for different clusters and the ZRZAMS values are listed as a function of α. on leave from Assumption College, Changanacherry, Kerala.     

Effects of rotation on the colours and line indices of stars 1. The alpha Persei cluster

Analysis of the available observational data for the α-Persei cluster members shows that rotation effects on the intermediate-band indices c₁ and (u-b) are considerable. In c₁, rotation produces a reddening of 0.040 magnitudes per 100 km s^-1 In (u-b) the effect for B stars is found to be 0.06 magnitudes per 100 km s^-1 ofV sin i. The binaries and peculiar stars are found to behave differently in the colour excess (due to rotation) versusV sin i diagrams. These empirical effects can be utilised to recalibrate these colour indices and also to separate members that are either chemically peculiar or in binary systems.