bluuebunny/crossref_metadata_2025_split huggingface dataset:
The acidity of trivalent cation-exchanged montmorillonite. II. Desorption of mono- and di-substituted pyridines
Authors: Breen C. 
Published: November 2006

AbstractTemperature programmed desorption (TPD) and IR spectroscopy were used to examine the desorption of pyridine, 2-methyl-, 4-methyl- and 2,6-dimethylpyridine from Al3+- and Cr3+-montmorillonite. Pyridine desorbed from Lewis sites at 150°C and from Bronsted sites at 340°C. 4-methylpyridine desorbed from Lewis and Bronsted centres at 210°C and 410°C respectively, some 60°C higher than pyridine due to its higher basicity. Conversely, the 2-methyl- and 2,6-dimethylpyridine, which are sterically hampered with respect to their coordination to Lewis centres, desorbed from these sites near 100°C, but due to their greater basicity desorbed from Bronsted sites at higher temperatures. These interpretations were confirmed by IR spectroscopy.
Preparation and characterization of iron oxide pillared montmorillonite
Authors: Doff D. H. , Gangas N. H. J. , Allan J. E. M. , Coey J. M. D. 
Published: November 2006

AbstractPillared smectites in which the pillars consist of iron oxide are expected to have interesting and unusual magnetic properties. Several possible routes by which such materials might be made have been investigated, namely intercalation of hydroxy-Fe(III) polycations, mixed hydroxy-Fe(III)/Al polycations, phenanthroline-Fe(II) cations, and trinuclear Fe(III) acetato cations into Na-montmorillonite. Only the last of these yielded a pillared clay (PILC) on calcination. The products have been characterized using X-ray powder diffraction and 57Fe Mössbauer spectroscopy. The precursor Fe-PILC has a d-spacing of 21 Å and expands to 23 Å on solvation with glycol. The calcined Fe-PILC has a d-spacing of 19 Å (gallery height 9·4 Å) and does not expand with glycol, confirming cross-linking of the layers. From Mössbauer spectra at 4·2 K it is estimated that there are of the order of some hundred Fe atoms per pillar.
The relation between the terra rossa and the carbonate-free residue of the underlying limestones and dolostones in Apulia, Italy
Authors: Moresi M. , Mongelli G. 
Published: November 2006

AbstractA statistical comparison has been made of chemical data for terra rossa and carbonate-free residues of Cretaceous limestones and dolostones in Apulia in order to evaluate the hypothesis that the terra rossa is a product of weathering of the underlying carbonate rocks. It has been shown that the differences in chemical composition between the residue of the carbonate rocks and the terra rossa are consistent with the former being the parent material of the latter. The transformation from carbonate rock residue to terra rossa was governed mainly by chemical weathering which produced a marked decrease in the K2O/Al2O3 (i.e. illite/kaolinite) ratio. The geochemical pattern of the Apulian terra rossa has been influenced by sedimentary processes which have led to a characteristic distribution of mineralogical components and a moderate contamination by biogenic silica.
Clay stability in clay-dominated soil systems
Authors: Righi D. , Velde B. , Meunier A. 
Published: November 2006

AbstractSeven samples from a chronosequence of soils developed in historically created polders on the Atlantic coast (Marais Poitevin, Vendée, France) were investigated in order to illustrate the rate of mineralogical change in a clay-dominated system. The oldest polder was constructed in 1665, the last one in 1912; thus the time span of soil evolution is from 80 to 330 years. All the samples had more than 50% clay (<2 μm). The most reactive, fine clay sub-fraction (<0.1 μm) was investigated in detail by X-ray diffraction and chemical analysis. The observed mineralogical changes with increasing age followed the schematic reaction:smectite + mica = illite + mixed-layer minerals.The progress of reaction in time appears to be non-linear. This reaction seems to occur in a chemically constant system, and the mineralogical change can be seen as a readjustment of species to a given chemical composition.
Acid dissolution of synthetic aluminous goethite before and after transformation to hematite by heating
Authors: Ruan H. D. , Gilkes R. J. 
Published: November 2006

AbstractMeasurements of the kinetics of acid dissolution of synthetic aluminous goethites and corresponding hematites produced by heating of parent Al-goethites at various temperatures were carried out in 1 M HC1 at 30, 40 and 50°C. Dissolution-time curves show sigmoidal shapes for the goethites (110°C), whereas deceleratory shapes were obtained for most of the partly and fully dehydroxylated samples. The dissolution rate for all materials decreased with increasing Al substitution and increased with increasing dissolution temperature, specific surface area and heating temperature. On a unit surface area basis, hematite dissolved ∼ 2–8 times faster than goethite. Dissolution kinetics of most heated goethite samples (200–260°C) were quite well described (R2 > 0.96) by the modified first-order Kabai equation. The activation energy and frequency factor for dissolution increased with increasing Al substitution.
Clay mineral variations associated with diagenesis and low-grade metamorphism of Early Cretaceous sediments in the Cameros Basin, Spain
Authors: Barrenechea J. F. , Rodas M. , Mas J. R. 
Published: November 2006

AbstractThe clay mineral distribution in the Early Cretaceous depositional sequences along the Cameros Basin has been established on the basis of XRD traces and TEM/EDAX analyses. Samples from the Latest Berriasian-Barremian depositional sequences are characteristic of epimetamorphic conditions. Illite ‘crystallinities’ are broader than expected (0.35–0.490°Δ2θ), due to the consistent presence of K-mica-paragonite mixed-layer and discrete paragonite associated with the illite 10 Å peak. The Late Barremian-Early Aptian depositional sequence, around the depocentral sector of the basin, represents a sudden change to anchimetamorphic conditions, marked by the presence of pyrophyllite and rectorite and by a significant decrease in the A1IVcontent of the chlorites. Towards the northwestern border of the basin, this sequence was affected by deep diagenetic conditions, as deduced from the clay mineral association and the ‘crystallinity’ values (0.57°Δ2θ). The changes in the clay mineral assemblages and ‘crystallinity’ data can hardly be explained in terms of the varying burial depth and are related to changes in the circulation of fluids associated with varying facies (modal composition, grain size). Permeability is regarded as the main factor controlling the circulation of these migratory fluids.
Detailed study of smectite genesis in granitic saprolites by analytical electron microsopy
Authors: Aoudjit H. , Robert M. , Elsass F. , Curmi P. 
Published: November 2006

Abstract: Smectite genesis in two granitic saprolites was studied, using qualitative and quantitative mineralogical methods and high resolution transmission electron microscopy (HRTEM). The primary minerals (plagioclase and mica) give rise to the formation of different kinds of smectites according to the weathering conditions (pH and drainage). Under a relatively basic, drained environment, a neoformed montmorillonite with a spheroidal organization exists in fillings of plagioclase cores. In the same conditions biotites are transformed into beidellites with a quasi-crystal organization. Under hydromorphic conditions, muscovites evolve incompletely towards smectites, whereas biotites lead to a montmorillonite with a tactoid organization.
ESCA and solid-state NMR studies of allophane
Authors: He N. , Barr T. L. , Klinowski J. 
Published: November 2006

AbstractThe surface/near-surface chemistry of allophane has been studied by X-ray photoelectron spectroscopy (ESCA) and the bulk material by 27A1 and 29Si solid-state NMR and other techniques. The surface/near-surface Si/Al ratio of allophane is c.1.0, similar to that for kaolinite, zeolite Na-A and sodalite. The core level binding energies for kaolinite and allophane are almost identical, but quite different from those for zeolite Na-A and sodalite, both framework aluminosilicates. The nature and size of these differences is consistent with the differences between the chemistry of sheet and framework silicates. The small variations in the Si(2p) spectra for kaolinite and allophane are discussed in terms of bonding of the tetrahedral units in the two materials.
REE distribution in presentday and ancient surface environments of basaltic rocks (Central Portugal)
Authors: Prudêncio M. I. , Gouveia M. A. , Sequeira Braga M. A. 
Published: November 2006

AbstractRare earth elements are mobilized, fractionated and precipitated during weathering processes of basaltic rocks of the Lisbon Volcanic Complex. In general there is an increase in the REE contents in the whole samples with increasing weathering and fractionation between LREE and HREE. Cerium is partially oxidized and Ce4+ is retained resulting in negative Ce anomalies in the whole samples of the base and middle profile zones. In the clay fraction there is an increase in the REE contents from the top to the bottom of the profiles, except for Ce, giving rise to positive Ce anomalies in the top and negative anomalies of this element in the middle and bottom of the profiles. Significant positive Ce anomalies occur in the finer fractions of palaeoweathered (Upper Cretaceous/ Lower Eocene) basalts associated with low REE contents relative to the whole samples indicating more intense leaching conditions in the Upper Cretaceous/Lower Eocene than at the present day. However, in both cases no positive Ce anomalies were found in the whole samples. There appears to be a negative correlation between the (La/Yb)ch ratio variation and the clay mineralogy/drainage conditions.
The 1640 cm-1 infrared band, monitor for the gain and thermal stability of water produced in ground kaolinites
Authors: Mendelovici E. , Villalba R. , Sagarzazu A. , Carias O. 
Published: November 2006

AbstractThe development of the infrared (IR) absorption band at 1640 cm−1 (δH2O) is employed to monitor the gain in molecular water of progressively mortar-ground kaolinite. The planimetred area of this band shows a linear correlation with weight loss at 105°C (free moisture) between 2 and 18 h grinding, indicating a steady increase of molecular water in this range. Heating of ground products to 105°C causes a decrease of about ⅓ in the 1640 cm−1 peak area for all ground samples. This area decrease corresponds to a 34% (average) loss of free moisture as determined by gravimetry. The remaining water is held up to 280°C and is more tightly held in the kaolinite ground for shorter (2–5 h) intervals than in further ground kaolinites. The 1640 cm−1 peak is not detected in any ground kaolinite after heating to 600°C the temperature at which kaolinite dehydroxylates completely. The differentiation of the energetically different OH groups present in ground kaolinite and the mechanism of water gain are compared and discussed from IR spectroscopy and weight loss results.
Etude comparee des complexes hectorite- et vermiculite-decylammonium a l'aide des spectrometries infrarouge et raman
Authors: Vimond-Laboudigue A. , Prost R. 
Published: November 2006

ResumeL'arrangement des cations décylammonium échangés entre les feuillets de la vermiculite et de l'hectorite a été précisé à l'aide des spectrométries infrarouge (IR) et Raman. Les expériences de deutération et de dichroïsme faites par spectrométrie IR montrent que l'axe C3 du groupe NH3+ est confondu avec l'axe de la cavité hexagonale sous-jacente, dans le cas de la vermiculite comme dans celui de l'hectorite, et que dans la vermiculite, les groupes NH sont engagés dans des liaisons hydrogène avec les atomes d'oxygène des tétraèdres substitués. La spectrométrie Raman permet de comparer l'arrangement des chaînes alkyles dans les deux phyllosilicates. En effet, cette technique donne accès à des modes de vibration très sensibles à la conformation des chaînes carbonées, en particulier grâce à la décomposition des bandes de vibration de valence des groupements CH2 et CH3. Ainsi, dans la vermiculite, on montre que les chaînes sont linéaires, et que leur arrangement interdigité est proche de celui du chlorure de décylammonium cristallisé. Les spectres Raman obtenus pour l'hectorite mettent en évidence l'existence de conformations gauches dans les chaînes alkyles, qui caractérisent une rotation de la chaîne autour de la liaison C-C voisine du groupe NH3+ terminal. Les résultats obtenus en Raman montrent par ailleurs que les interactions entre les chaînes alkyles sont beaucoup plus faibles que dans le cas de la vermiculite et confortent le modèle proposé ici pour le complexe hectorite-décylammonium, pour lequel les chaînes sont parallèle aux surfaces des feuillets.
Clay mineral evolution in the Illinois Basin and its causes
Authors: Gharrabi M. , Velde B. 
Published: November 2006

AbstractSamples from deep wells of the Palaeozoic Illinois Basin show the evolution of the illite-smectite (I-S) mineral transformation under low temperatures for very long periods of time. Curve decomposition of the XRD traces was used to identify and follow the evolution of the different clay minerals. All samples showed the presence of a large amount of illite (fine and coarse grained micaceous material) and a much smaller quantity of I-S. In a vertical section the R=1, I-S diffraction peak initially changes with depth indicating change from 80 to 95% illite content but it changes little with further depth. The I-S intensity decreases with depth compared with the illite peaks. These relations indicate that the clays in the Palaeozoic sequence of the Illinois Basin evolve continuously in the deep well, It appears that the final stages of I-S mineral transformation can reach a compositional stagnation (smectite content) as the I-S phase is dissolved to produce illite.Using a kinetic model to describe the smectite to illite clay transformation, it is deduced that the Illinois basin had a longer period of deposition than indicated by present stratigraphy and that almost 1.5 km of sediments deposited in the Mesozoic were eroded in later Tertiary times. These conclusions are confirmed by published data on the maturation of organic matter.
Mineralogy and geochemistry of Devonian detrital rocks from the Iberian Range (Spain)
Authors: Bauluz Lazaro B. , Mayayo Burillo M.J. , Fernandez-Nieto C. , Gonzalez Lopez J.M. 
Published: November 2006

AbstractTwo profiles in Devonian marine deposits have been studied, consisting of pelites, subgreywackes, greywackes and quartzites. Quartz and clay minerals are major components and feldspar and calcite are minor ones. Phyllosilicates in the fine fractions are kaolinite and illite; kaolinite has a high degree of ordering; illite is predominantly of a 1Md polytype, with low Na content and poor crystallinity and has a phengitic composition in greywackes, whereas in pelites it is muscovitic in composition. Both phyllosilicates may be inherited from a source area with intensive weathering processes, although illite may also be a diagenetic phase. These mineral characteristics indicate that the Devonian rocks did not reach the anchizone boundary in their post-depositional evolution.The chemical composition of pelites and subgreywackes reveals a high degree of chemical maturity. Chondrite-normalized REE patterns indicate a higher degree of weathering of these Devonian sediments than of Post-Archaean Australian Shales (PAAS), possibly as a consequence of sedimentary recycling processes. The REE patterns of the Devonian rocks in addition to the high Th/Sc, La/Sc and Th/Co ratios suggest a felsic composition of the primitive source area, probably a K-rich granite.
Comparative study of the transition between very low-grade and low-grade metamorphism in siliciclastic and carbonate sediments: Early Cretaceous, Cameros Basin (northern Spain)
Authors: Alonso-Azcarate J. , Barrenechea J. F. , Rodas M. , Mas J. R. 
Published: November 2006

AbstractThe transition between very low-grade and low-grade metamorphism has been studied in the Urbión and Enciso Groups of the Late Jurassic-Early Cretaceous Cameros basin (NE Spain). The ‘illite crystallinity’ (IC) values do not appear to be controlled by burial depth but rather by: (1) XRD overlap with other phases (e.g. paragonite and mixed-layered muscovite-paragonite) in the siliciclastic samples; (2) the presence of carbonates, which delay illitization, resulting in an increase in the IC values, that becomes more pronounced as the P-T conditions decrease towards the diagenesis zone; and (3) the permeability of the sediments, which controls the circulation of metamorphic fluids and therefore the distribution of ‘crystallinities’ and mineral assemblages within the basin.The anchizone is represented by a narrow range of ‘chlorite crystallinity’ (ChC) values. Therefore, ChC is a less sensitive parameter than IC for estimating changes from diagenetic to low-grade metamorphic conditions. However, ChC can be a useful tool when there is a great heterogeneity of facies types, as it is not affected by the presence of carbonates.
Systematic assignment of thermodynamic constraints in metabolic network models
Authors: Kümmel Anne , Panke Sven , Heinemann Matthias 
Published: November 2006

Abstract

Background
The availability of genome sequences for many organisms enabled the reconstruction of several genome-scale metabolic network models. Currently, significant efforts are put into the automated reconstruction of such models. For this, several computational tools have been developed that particularly assist in identifying and compiling the organism-specific lists of metabolic reactions. In contrast, the last step of the model reconstruction process, which is the definition of the thermodynamic constraints in terms of reaction directionalities, still needs to be done manually. No computational method exists that allows for an automated and systematic assignment of reaction directions in genome-scale models.

Results
We present an algorithm that – based on thermodynamics, network topology and heuristic rules – automatically assigns reaction directions in metabolic models such that the reaction network is thermodynamically feasible with respect to the production of energy equivalents. It first exploits all available experimentally derived Gibbs energies of formation to identify irreversible reactions. As these thermodynamic data are not available for all metabolites, in a next step, further reaction directions are assigned on the basis of network topology considerations and thermodynamics-based heuristic rules. Briefly, the algorithm identifies reaction subsets from the metabolic network that are able to convert low-energy co-substrates into their high-energy counterparts and thus net produce energy. Our algorithm aims at disabling such thermodynamically infeasible cyclic operation of reaction subnetworks by assigning reaction directions based on a set of thermodynamics-derived heuristic rules. We demonstrate our algorithm on a genome-scale metabolic model of E. coli. The introduced systematic direction assignment yielded 130 irreversible reactions (out of 920 total reactions), which corresponds to about 70% of all irreversible reactions that are required to disable thermodynamically infeasible energy production.

Conclusion
Although not being fully comprehensive, our algorithm for systematic reaction direction assignment could define a significant number of irreversible reactions automatically with low computational effort. We envision that the presented algorithm is a valuable part of a computational framework that assists the automated reconstruction of genome-scale metabolic models.
Comparison of human uterine cervical electrical impedance measurements derived using two tetrapolar probes of different sizes
Authors: Gandhi Saurabh V , Walker Dawn C , Brown Brian H , Anumba Dilly OC 
Published: November 2006

Abstract

Background
We sought to compare uterine cervical electrical impedance spectroscopy measurements employing two probes of different sizes, and to employ a finite element model to predict and compare the fraction of electrical current derived from subepithelial stromal tissue.

Methods
Cervical impedance was measured in 12 subjects during early pregnancy using 2 different sizes of the probes on each subject.

Results
Mean cervical resistivity was significantly higher (5.4 vs. 2.8 Ωm; p < 0.001) with the smaller probe in the frequency rage of 4–819 kHz. There was no difference in the short-term intra-observer variability between the two probes. The cervical impedance measurements derived in vivo followed the pattern predicted by the finite element model.

Conclusion
Inter-electrode distance on the probes for measuring cervical impedance influences the tissue resistivity values obtained. Determining the appropriate probe size is necessary when conducting clinical studies of resistivity of the cervix and other human tissues.
A study of association between common variation in the growth hormone-chorionic somatomammotropin hormone gene cluster and adult fasting insulin in a UK Caucasian population
Authors: Freathy Rachel M , Mitchell Simon MS , Knight Beatrice , Shields Beverley , Weedon Michael N , Hattersley Andrew T , Frayling Timothy M 
Published: November 2006

Abstract

Background
Reduced growth during infancy is associated with adult insulin resistance. In a UK Caucasian cohort, the CSH1.01 microsatellite polymorphism in the growth hormone-chorionic somatomammotropin hormone gene cluster was recently associated with increases in adult fasting insulin of approximately 23 pmol/l for TT homozygote males compared to D1D1 or D2D2 homozygotes (P = 0.001 and 0.009; n = 206 and 92, respectively), but not for females. TT males additionally had a 547-g lower weight at 1 year (n = 270; P = 0.008) than D2D2 males. We sought to replicate these data in healthy UK Caucasian subjects. We genotyped 1396 subjects (fathers, mothers and children) from a consecutive birth study for the CSH1.01 marker and analysed genotypes for association with 1-year weight in boys and fasting insulin in fathers.

Results
We found no evidence for association of CSH1.01 genotype with adult male fasting insulin concentrations (TT/D1D1 P = 0.38; TT/D2D2 P = 0.18) or weight at 1 year in boys (TT/D1D1 P = 0.76; TT/D2D2 P = 0.85). For fasting insulin, our data can exclude the previously observed effect sizes as the 95 % confidence intervals for the differences observed in our study exclude increases in fasting insulin of 9.0 and 12.6 pmol/l for TT relative to D1D1 and D2D2 homozygotes, respectively. Whilst we have fewer data on boys' 1-year weight than the original study, our data can exclude a reduction in 1-year weight greater than 557 g for TT relative to D2D2 homozygotes.

Conclusion
We have not found association of the CSH1.01 genotype with fasting insulin or weight at 1 year. We conclude that the original study is likely to have over-estimated the effect size for fasting insulin, or that the difference in results reflects the younger age of subjects in this study relative to those in the previous study.