bluuebunny/crossref_metadata_2025 huggingface dataset:
Delayed Blood Pressure Recovery After Psychological Stress Is Associated With Carotid Intima-Media Thickness
Authors: Steptoe Andrew , Donald Ann E. , O’Donnell Katie , Marmot Michael , Deanfield John E.
Published: August 2006

Objective—

Delayed blood pressure (BP) recovery after psychological stress is associated with low socioeconomic status (SES) and prospectively with increases in clinic BP. We tested whether poststress BP recovery was related to carotid atherosclerosis.

Methods and Results—

Psychophysiological stress testing was performed with a healthy subgroup of the Whitehall II epidemiological cohort, and recovery systolic BP was monitored 40 to 45 minutes after stressful behavioral tasks. Carotid ultrasound scanning was conducted on 136 men and women (aged 55.3±2.7 years) 3 years after stress testing. Participants were divided into those whose systolic BP had returned to baseline in the recovery period (adequate recovery, n=37), and those whose BP remained elevated (delayed recovery, n=99). Systolic BP stress responses did not differ in the 2 groups. Carotid intima-media thickness (IMT) was associated with delayed recovery in lower SES (means 0.78 versus 0.65 mm) but not higher SES participants (means 0.75 versus 0.74 mm) after adjustment for age, gender, baseline systolic BP, and resting BP, smoking, body mass and fasting cholesterol at the time of ultrasound scanning (
P
=0.010).

Conclusions—

Variations in poststress recovery reflect dysfunction of biological regulatory processes, and may partly mediate psychosocial influences on cardiovascular disease.
Influence of Atorvastatin Treatment on
l
-Arginine Cerebrovascular Reactivity and Flow-Mediated Dilatation in Patients With Lacunar Infarctions
Authors: Pretnar-Oblak Janja , Sabovic Miso , Sebestjen Miran , Pogacnik Tomaz , Zaletel Marjan
Published: August 2006

Background and Purpose—

In our study we hypothesized that statins improve endothelial function in patients with lacunar infarctions (LI). Cerebral and systemic endothelial function was determined before and after 3-months treatment with atorvastatin.

Methods—

Cerebral endothelial function was determined by
l
-arginine reactivity and systemic endothelial function by flow-mediated dilatation (FMD) in patients with LI (18 patients, aged 61.1±7.6 years), 20 age- and gender-matched patients with similar risk factors (SR) and 19 age- and gender-matched healthy controls. The mean arterial velocity (v
m
) in both middle cerebral arteries was measured by transcranial Doppler sonography before, during and after a 30-minute intravenous infusion of
l
-arginine. FMD of the brachial artery after hyperaemia was determined. The measurements were repeated after 3-months treatment with 40 mg of atorvastatin per day.

Results—

l
-arginine reactivity was decreased in LI patients (13.1±8.4%) and in patients with SR compared with healthy controls (
P
≤0.01). FMD was more impaired in patients with LI (0.06±4.9%) compared with patients with SR and healthy controls (
P
≤0.01). After atorvastatin treatment,
l
-arginine reactivity and FMD improved in both patients with LI (17.1±7.6%; 7.0±5.7%) and patients with SR (
P
≤0.01). Previously mildly increased cholesterol values normalized.

Conclusion—

The decreased
l
-arginine reactivity and FMD improve after atorvastatin treatment in both patients with LI and patients with SR.
Frequency and Determinants of Nonpublication of Research in the Stroke Literature
Authors: Sanossian Nerses , Ohanian Arbi G. , Saver Jeffrey L. , Kim Linda I. , Ovbiagele Bruce
Published: August 2006

Background and Purpose—

Selective nonpublication will yield publication bias and a published literature imperfectly representative of the full range of scientific findings. We evaluated the proportion of research abstracts presented at the leading United States research meeting in stroke, the International Stroke Conference (ISC), which were subsequently published as full-length articles and investigated the factors associated with full manuscript publication.

Methods—

Features of all abstracts presented at the annual ISC meeting in February 2000 were analyzed. Search of the National Library of Medicine PubMed database and written communication with abstract authors was performed to determine conversion of abstracts to fully published manuscripts over the subsequent 5 years.

Results—

Among the 353 abstracts presented at the 2000 International Stroke Conference, 108 were oral presentations and 245 posters. Overall, 202/353 (62.3%) resulted in full-length publications, with a median time to publication of 15 months. In multivariate analysis, factors increasing likelihood of full-length publication were: platform rather than poster presentations (odds ratio [OR] 3.0, 95% CI, 1.6 to 5.5), authors with a university affiliation (OR 2.2, 95% CI, 1.2 to 4.1), and European region of origin (OR 2.2, 95% CI, 1.1 to 4.4), whereas topic concerning community/risk factors decreased the likelihood of publication (OR 0.3, 95% CI, 0.16 to 0.74). Positive results, multicenter collaboration and industry sponsorship did not affect publication rate.

Conclusions—

Approximately 1 of every 3 abstracts presented at an international stroke meeting was not published as a full manuscript within 5 years. Poster abstracts were less likely to be published in full manuscript form than oral presentations.
Demographic life history traits of reproductive natterjack toads (Bufo calamita) vary between northern and southern latitudes
Authors: Sanuy Delfi , Leskovar Christoph , Oromi Neus , Sinsch Ulrich
Published: August 2006

Demographic life history traits were investigated in three Bufo calamita populations in Germany (Rhineland-Palatinate: Urmitz, 50°N; 1998-2000) and Spain (Catalonia: Balaguer, Mas de Melons, 41°N; 2004). We used skeletochronology to estimate the age as number of lines of arrested growth in breeding adults collected during the spring breeding period (all localities) and during the summer breeding period (only Urmitz). A data set including the variables sex, age and size of 185 males and of 87 females was analyzed with respect to seven life history traits (age and size at maturity of the youngest first breeders, age variation in first breeders, longevity, potential reproductive lifespan, median lifespan, age-size relationship). Spring and summer cohorts at the German locality differed with respect to longevity and potential reproductive lifespan by one year in favour of the early breeders. The potential consequences on fitness and stability of cohorts are discussed. Latitudinal variation of life history traits was mainly limited to female natterjacks in which along a south-north gradient longevity and potential reproductive lifespan increased while size decreased. These results and a review of published information on natterjack demography suggest that lifetime number of offspring seem to be optimized by locally different trade-offs: large female size at the cost of longevity in southern populations and increased longevity at the cost of size in northern ones.
Sexual size dimorphism in the Cuban treefrog Osteopilus septentrionalis
Authors: Vargas-Salinas Fernando
Published: August 2006

To find out the main cause of the sexual size dimorphism (SSD) in the Cuban treefrog Osteopilus septentrionalis, I studied between April 2002 and April 2004 the breeding behavior and survival of individuals in a population localized in north-western Puerto Rico, West Indies. This species is an explosive breeder whose breeding events lasted one night. Mature females were larger in body size (snout vent-length, SVL) (range 57-107 mm) than mature males (range 41.5-67 mm), and exhibited higher levels of survival (males: 0.72, 95% confidence interval 0.66-0.78; females 0.91, 95% confidence interval 0.88-0.93). Females can increase their reproductive success if they breed with large SVL because large females can lay more eggs than small females. In contrast, the reproductive success of males was not enhanced by large SVL because the mating pattern was random and non-assortative by SVL. Thus, for males it could be better to start to breed with small SVL, and participate in all possible breeding events, which implies high mortality risk. As a consequence, the SSD in O. septentrionalis may be due to fecundity advantages in females, and because males tend to die before reaching larger SVL.
A Re-analysis of the phylogeny of the genus Protobothrops (Reptilia: Viperidae), with particular reference to the systematic position of P. xiangchengensis
Authors: Guo Peng , Zhao Ermi , Zhang Yaping , Pang Junfeng
Published: August 2006

Based on three mitochondrial gene fragments (12S rRNA, 16S rRNA, cytochrome b), the phylogeny of Protobothrops is re-analyzed using Maximum-parsimony (MP), Maximum-likelihood (ML), and Bayesian (BI) approaches. All phylogenetic analyses indicate that all putative Protobothrops species examined formed a monophyletic group; however, the intrageneric relationships are still unresolved. The phylogenetic relationships further confirm that P. xiangchengensis is a valid species distinct from P. mucrosquamatus and that it is closely related to P. jerdonii.
Habitat use during the aquatic phase of the newts Triturus vulgaris (L.) and T. cristatus (Laurenti) in central Norway: proposition for a conservation and monitoring area
Authors: Skei Jon , Ringsby Thor , Rønning Lars , Dolmen Dag
Published: August 2006

Amphibian populations are declining at an alarming pace in many parts of the world. Consequently, as part of the strategy for establishing a 360 km2 conservation and reference area for amphibians in central Norway, 341 lentic water bodies were surveyed to investigate and briefly describe their hydrography and the occurrence of the newts Triturus vulgaris (L.) and T. cristatus (Laurenti) in the area. In particular we investigated the factors that could explain the presence of the respective newt species, including biotic and abiotic factors. The multiple logistic regression analyses suggested that the presence of T. cristatus was best explained by altitude and ion concentration, both in a nonlinear fashion, whereas fish had a negative effect on T. cristatus, which was never found coexisting with fish. The presence of T. vulgaris was best explained by altitude (linear relationship) and ion concentration (convex relationship), besides the occurrence of T. cristatus. Triturus vulgaris was occasionally found to occur at low densities in ponds having fish. For both species the probability of presence was higher when the opposite newt species was present. pH influenced both species in a convex nonlinear fashion with highest probability of presence around pH 6.5. This area is valuable for conservation, monitoring and reference for marginal amphibian populations. Any decline in their abundance would be discovered relatively quickly, and likely causes could be inferred. It can also serve as a reference area for future comparative studies of amphibians elsewhere.
Body temperature of free-living freshwater turtles, Hydromedusa maximiliani (Testudines, Chelidae)
Authors: Martins Fernando , Souza Franco
Published: August 2006

Field body temperatures of the Maximilian's snake-necked turtle, Hydromedusa maximiliani, a small freshwater turtle species endemic to Atlantic rainforest mountainous regions in Brazil, were studied. Turtle body temperatures and water temperatures were significantly related, but turtle body temperature averaged 1°C higher than stream water temperature, this difference being statistically significant. A multivariate model revealed that only water temperature was significantly related to turtle body temperature while body size had no effect. There was no effect of sex and life stage on turtle body temperature, implying that water temperature was the main factor determining body temperatures. Thermoconformity was verified for all sampled individuals. The broad implications of these results are also discussed.
Redescription of Leptotyphlops koppesi Amaral, 1954, and description of a new species of the Leptotyphlops dulcis group from Central Brazil (Serpentes: Leptotyphlopidae)
Authors: Passos Paulo , Caramaschi Ulisses , Pinto Roberta
Published: August 2006

A new species of Leptotyphlops dulcis group is described from the central Brazilian Cerrado, which is diagnosed by rostral shape, general colour pattern, and number of middorsal and subcaudal scales. This taxon has been commonly misidentified as L. koppesi in some Brazilian collections and by some authors. Leptotyphlops koppesi was described from the municipality of Terenos, State of Mato Grosso do Sul, Brazil, based on a single specimen. Since its original description, only three subsequent records appear in the literature reporting additional specimens of L. koppesi. We redescrib the holotype of Leptotyphlops koppesi, defining its geographic range and diagnose this from all species of L. dulcis group. Data on morphometric and meristic variation are reported for the new species and L. koppesi as well. Comparisons are made between the new species and all other South American species of the L. dulcis group. The hemipenis of the new species has a narrow basal portion and a series of lateral flounces. This general hemipenial morphology is unique among Neotropical leptotyphlopids, otherwise known only from Atlantic Rainforest species L. salgueiroi.
Growth and age of the southernmost distributed gecko of the world (Homonota darwini) studied by skeletochronology
Authors: Piantoni Carla , Cussac Victor , Ibargüengoytía Nora
Published: August 2006

Homonota darwini is the southernmost distributed gekkonid species of the world, as it can be found in South America from 35° to 52°S. Age and growth of H. darwini were studied using skeletochronology on diaphyseal femoral cross-sections. Individual ages were assessed after estimating the resorbed rings in relation to snout-vent length (SVL). SVL and age showed a sigmoidal relationship and growth rates showed a shift from premature growth to mature breeding when sexual maturity is achieved. The model indicates that sexual maturity in H. darwini is reached at five years in females and nine in males. Species longevity is estimated to be 17 years, which corresponds to a k-selected trait of late maturity and long life expectancy. Once sexual maturity is achieved, size is a poor indicator of age in this species. These results are discussed in terms of behavioural and physiological adaptations of this species to the strong environmental pressures of the Patagonian steppe. Our results also support the hypothesis that daytime burrow temperatures, which are similar to body temperatures recorded in diurnal lizard species, meet the physiological growth requirements of nocturnal lizard species.
Comparing Nations and States
Authors: Beer Caroline , Mitchell Neil J.
Published: August 2006

Democracy and the protection of human rights generally go together, but not in India. India is an outlier in the cross-national research that aims to explain human rights performance. Using state-level subnational data and drawing on the approaches pioneered at the cross-national level, the authors examine the reasons for the outlier status. Their findings suggest that the aggregate whole-nation human rights and democracy scores misrepresent the political experience of much of India. The authors find that participation, political parties, and the level and nature of opposition threat help us understand the incidence of human rights violations within India.
Mobilizing Political Talk in a Presidential Campaign
Authors: Pan Zhongdang , Shen Lijiang , Paek Hye-Jin , Sun Ye
Published: August 2006

This article takes a talk-centered perspective on a mediated presidential campaign. It argues that election campaigns can be conceived of as collective deliberations and that informal political talk during a campaign may be examined as an analytical category in its own right. Analyzing the National Election Study 2000 panel data ( n = 1,555), this article shows that political talk during the campaign was prevalent. Both the likelihood and frequency of engaging in political talk during the campaign were related to individuals’ propensity to participate in public life and resulted from individuals’ ideological intensity and interest in the campaign. The campaign also stimulated such political talk through individuals’ exposure to campaign messages and other-initiated campaign contacts. General news media uses contributed to more political talk and campaign participation indirectly by increasing the frequency of exposure to campaign messages on media. Theoretical implications for the research on political campaigns in particular and media effects in general are discussed.
JAZ mediates G1 cell-cycle arrest and apoptosis by positively regulating p53 transcriptional activity
Authors: Yang Mingli , Wu Song , Su Xuekun , May W. Stratford
Published: August 2006

We previously identified JAZ as a novel zinc finger (ZF) protein by screening a murine interleukin-3 (IL-3)–dependent NFS/N1.H7 myeloid cell cDNA library. JAZ is a member of a new class of ZFPs that is evolutionarily conserved and preferentially binds to dsRNA, but its function was unknown. Now, we report that the stress of IL-3 growth factor withdrawal up-regulates JAZ expression in hematopoietic cells in association with p53 activation and induction of cell death. Biochemical analysis reveals that JAZ associates with p53 to stimulate its transcriptional activity in p53-expressing cells, but not in p53-null cells unless complemented with p53. JAZ functions to mediate G1 cell-cycle arrest followed by apoptosis in a p53-dependent mechanism that is associated with up-regulation of p21 and BAX, dephosphorylation of Rb, and repression of cyclin A. Of importance, siRNA “knockdown” of endogenous JAZ inhibits p53 transcriptional activity, decreases the G1/G0 population, and attenuates stress-induced cell death. While JAZ directly binds p53 in vitro in a mechanism requiring p53's C-terminal regulatory domain but independent of dsRNA, the dsRNA-binding ZF domains are required for JAZ's stimulatory role of p53 in vivo by dictating its nuclear localization. Thus, JAZ is a novel negative regulator of cell growth by positively regulating p53.
Mineralogy and Geology of the Maungaparerua Halloysite Deposit in New Zealand
Authors: Murray Haydn H. , Harvey Colin , Smith John M.
Published: August 2006

The Maungaparerua halloysite deposit is located on the North Island of New Zealand some 210 km north of Auckland. The halloysite deposit was formed by hydrothermal alteration of rhyolite flow rocks. Superimposed on the hydrothermally altered halloysite is deep intensive surficial weathering resulting from the humid climate on the extreme tip of the North Island. The deposit has been drilled and the cores have been analyzed mineralogically and chemically. Drilling has shown that the deposit is circular or ovate and covers about 350 acres. The altered rocks contain about 50% quartz and fine amorphous silica and 50% of a mix of halloysite, kaolinite, and allophane with a small amount of plagioclase feldspar in the coarse fraction. The upper 8–30m, with an average of 15m, of the halloysite alteration deposit consists of relatively soft clay. Below this soft clay, which is the result of intense surficial weathering, the clay becomes hard and dense. The halloysite and kaolin from this deposit are mined and beneficiated using wet process techniques of dispersion, centrifugation, leaching, dewatering, and drying. The products are used as filler in paper, paint, and plastics and as a ceramic raw material for producing whiteware and fine china. This deposit is unique in that it contains a very high proportion of halloysite in the clay fraction. The detailed geology, mineralogy, geochemistry, and the physical properties of the clay will be discussed.
Adsorbed Molecules on Solvated Layer Silicates: Surface Mobility and Orientation from ESR Studies
Authors: McBride M. B.
Published: August 2006

The adsorption of nitroxide spin probes on smectites solvated in liquids of greatly different polarity was studied using electron spin resonance (ESR) spectroscopy. Adsorbed probes demonstrate various degrees of restricted rotational motion and alignment at the silicate surfaces, depending upon the properties of the solvating liquid. The results are interpreted in terms of direct surface—molecule interaction modified by solvent competition effects. A fraction of the probe molecules is immobilized in many of the solvated clays because of small spacings between platelets. The data indicate lowered reactivity of surface-adsorbed molecules, especially in the case of hydrated smectites.
Adsorption of Safranine by Na+, Ni2+ and Fe3+ Montmorillonites
Authors: Van Damme H. , Crespin M. , Cruz M. I. , Fripiat J. J.
Published: August 2006

The adsorption of the cationic oxidized safranine S+ by a Na+, Ni2+ and Fe3+ montmorillonite has been studied with X-ray powder diffraction, u.v., visible and i.r. spectroscopy. In solution S+ may be protonated: S+, SH2+ and SH23+ have characteristic spectra in the 500–600 nm region where the clay structure does not absorb. In the Na+ as well as in the Ni2+ and Fe3+ clays, the adsorption of S+ is a cation exchange process accompanied by the protonation of the adsorbed dye such as variable concentrations of M+ (Na+, Ni2+ or Fe3+), S+ and SH2+ are simultaneously present. Protonation activity decreases from Fe3+ to Ni2+ and Na+, being the protonation site the amine group as shown by i.r. In the interlamellar space it seems that a SH2+.. S+ association exists that could be described as a sandwich structure 6.5 Å thick.
Quantitative Analysis of Elements in Sediments and Soils by X-Ray Fluorescence
Authors: Tuncer E. R. , Demirel T. , Lohnes R. A.
Published: August 2006

Previous applications of the method of known additions for quantitative X-ray fluorescent analysis have assumed a linear relationship between peak intensity and concentration of the element being analyzed. This assumption is true for soils or sediments containing small amounts of the element in question. In this paper, an equation is derived which takes into account both absorption and enhancement and thus is applicable to samples containing high concentrations of the element. The equation was tested by analyzing an artificial soil sample containing 60% kaolinite and 40% hematite, i.e. the sample contained 28% by weight iron. The fluorescent analysis utilizing the equation derived here resulted in an iron content of 27%. In addition, nine soils from Hawaii were analyzed by this method and the results of these analyses compared with analyses by atomic absorption. The agreement between the two methods is good. It is concluded that the method and equations proposed here provides a reliable measurement of elements in a soil sample which contains high concentrations of the elements in question.
Clay Mineralogy in Relation to Deltaic Sedimentation Patterns of Desmoinesian Cyclothems in Iowa-Missouri
Authors: Brown L. F. , Bailey S. W. , Cline L. M. , Lister Judith S.
Published: August 2006

Almost four decades of study of Desmoinesian strata of Middle Pennsylvanian age in south-central Iowa and north-central Missouri have provided the stratigraphic control required to test the variation of clay mineralogy vertically and laterally within various paralic clay and shale facies. Local and regional variations in clay mineralogy within Desmoinesian strata are generally predictable and are in agreement with current knowledge of deltaic deposition. A principal environmental variation within a deltaic system is the change from normal marine salinities in deltaic marine environments to brackish- and fresh-water conditions in the marshy delta plains, in upper interdistributary bays, and within flanking interdeltaic embayments. Changes from marine to nonmarine facies coincide with a decrease in illite, and an increase in kaolin, mixed-layer clays, and in the percentage of expansible layers in the mixed-layer clay. The principal clay detritus entering the area was illite, which underwent various degrees of alteration in different aqueous and subaerial environments within deltaic and interdeltaic areas. Clay-mineral composition alone does not provide unique environmental answers. The distribution of clay-mineral suites within these systems, however, both supports the deltaic-interdeltaic depositional model and can be understood within the context of this framework.
Change of b-Dimension with Swelling of Montmorillonite
Authors: Ravina Israela , Low Philip F.
Published: August 2006

The effect of swelling on the b-dimension of Na-saturated, Upton, Wyoming montmorillonite was re-examined using powdered silicon as an internal standard. After being corrected with reference to the internal standard, the b-dimension did not increase through the entire range of swelling as reported previously. It increased up to a water content of ~3.0g/g montmorillonite and remained constant thereafter. However, the diffraction peak of the internal standard shifted towards lower angles at higher water contents. This shift was attributed to a relaxation of the wetter samples away from the knife edge of the diffractometer. Presumably, a similar relaxation occurred in the earlier study and was responsible for the apparent increase in b-dimension at water contents above ~3.0g/g.

The b-dimension of Upton montmorillonite saturated with different cations was determined using powdered silicon and a colloidal quartz impurity as internal standards. The water content at maximal swelling decreased as the b-dimension increased.
Synthetic Kaolinites Doped with Fe2+ and Fe3+ Ions
Authors: Angel B. R. , Cuttler A. H. , Richards K. S. , Vincent W. E. J.
Published: August 2006

Previous studies by Electron Spin Resonance (ESR) have established the substitution of Fe3+ and Mg2+ in the kaolinite structure. It is shown that Fe2+ can substitute in kaolinite and stabilize defects which are detectable by ESR in a manner identical to Mg2+. The development of methods of preparing a synthetic kaolinite doped with Fe2+ is described in detail. It is shown that the main ESR signals, which occur at g = 2.0 in natural kaolinites and which previously have been interpreted in terms of iron and magnesium, can be attributed to iron alone.
Identification of Tetramethylammonium Ion in Methylated NH4-Bentonite
Authors: Franco M. A. , Gessa C. , Cariati F.
Published: August 2006

Treating NH4-bentonite with diazomethane results in methylation of adsorbed ammonium with the formation of the tetramethylammonium ion. This ion, which can be completely removed through ion exchange, is distinguished in the IR spectrum by a strong band at 1480 cm−1 due to CH3 group bending vibrations. X-ray diffractograms, CEC, and surface area of the clay are not modified by treatment with diazomethane.
Scanning Electron Microscopy of Quartz in Precambrian Cherts and Dolomites from Southern Africa
Authors: le Roux J. , Jackson M. L.
Published: August 2006

Scanning electron microscopic (SEM) examination of the quartz isolated from chert of Transvaal and Swaziland, of 2000 and 3400 million year (MY) ages, respectively, in southern Africa revealed marked differences in quartz morphology. Well-defined individual euhedral quartz crystals, with polyhedral triple-point faces, were clearly evident on freshly fractured Transvaal chert surfaces as well as with the quartz isolates from the chert. The morphology and coarseness suggest crystal growth with little, if any, metamorphism; however, the δ18O values of 23.8–24.1‰ suggest crystallization temperatures of perhaps 40–45°C. In contrast, fracture surfaces of the older, strongly metamorphosed Swaziland cherts revealed a high degree of grain intergrowth which inhibited fracture between quartz grains. Quartz isolates from these showed strongly interlocked quartz crystal clusters and elongated chips of quartz with poorly defined irregular faces. Intercalation of mineral veins in the cherts on a mm scale and the intergrown character of the quartz grain boundaries provide evidence that the latter cherts have been strongly metamorphosed and recrystallized, in keeping with 14.6–15.1‰ δ18O values, corresponding to 80°C fractionation with water. The SEM micrographs of the fine quartz (1–10 µm) isolated from the Otavi dolomite formation of the 700-MY Damara System and from the 2000-MY Transvaal Dolomite Series revealed well-defined subhedral and euhedral quartz crystals of small size which, together with the 26.9–27.8‰ and 23.8‰ δ18O values, respectively, indicate that these dolomites have been affected little, if any, by post-depositional metamorphism; their crystallization temperatures fall in the range of 25–30 and 40–45°C, respectively.
Amorphous and Crystalline Titanium and Iron-Titanium Oxides in Synthetic Preparations, at Near Ambient Conditions, and in Soil Clays
Authors: Fitzpatrick R. W. , Le Roux J. , Schwertmann U.
Published: August 2006

A series of mixed iron and titanium oxide coprecipitates ranging in composition between 0 < Ti/Ti + Fe < 1 was synthesized and aged under varying conditions of pH, temperature and time in order to establish a working model for pedogenic titanium and titano-ferric oxides. X-ray powder diffraction (XRD), selective chemical dissolution, magnetic susceptibility, charge distribution and electron optical data indicate that the freshly prepared Fe-Ti oxides consist of an Fe-rich (Ti-ferrihydrite) phase (Ti/Ti + Fe ⩽ 0.70) having pH-dependent positive charge and a Ti-rich phase (Ti/Ti + Fe ⩾ 0.7) with permanent and pH dependent negative charge.

Synthetic Ti-ferrihydrite and amorphous TiO2 were completely soluble in acid ammonium oxalate (2 hr extraction in the dark) whereas poorly crystalline anatase (width at half height, WHH > 2.0°2θ) was partly oxalate soluble. NH4-oxalate soluble Ti was particularly high in soils developed under a cool montane climate (afro-alpine) and lower in soils of warmer subtropical climate, which contain anatase and rutile.

Several mixed Fe-Ti crystalline phases were identified after aging NH3 coprecipitates of Fe and Ti nitrate at 70°C and pH 5.5 for 70 days:

(1)

goethite and hematite in the composition range 0 < Ti/Ti + Fe ⩽ 0.20; at low Ti concentrations (<5 mole %) goethite was favored and/or hematite inhibited

(2)

microcrystalline pseudorutile in the composition range 0.20 ⩽ Ti/Ti + Fe ⩽ 0.70

(3)

anatase and ferriferous anatase in the range 0.70 ⩽ Ti/Ti + Fe < 1.0; with decreasing proportion of Ti the crystal-Unity of anatase decreased.

The results suggest that secondary or pedogenic Ti-Fe oxides can form by coprecipitation and crystallization in the weathering solution, and emphasize the essential role of water (as opposed to dry oxidation) in the alteration of primary titaniferous minerals.
Clay-Organic Molecule Interactions: Oxidation of Acetaldehyde by Montmorillonite in N2 Atmosphere at Room Temperature
Authors: Eltantawy I. M. , Baverez M.
Published: August 2006

Oxidation of acetaldehyde molecules adsorbed on Na- and Mg-Wyoming montmorillonite at room temperature (20-25°C) and in N2 atmosphere has been studied by I.R. spectroscopy, A comparison between clay-acetic acid complex and that prepared from acetaldehyde is given. The influence of the nature of the saturating cation as well as the clay pretreatment on this oxidation process are discussed and reaction pathways are proposed. Acetic acid directly adsorbed on the clay surface is almost removed at 110°C, while that produced from the oxidation of the adsorbed acetaldehyde appears to be strongly held. Within a temperature range 180-230°C, the fixed acetic acid molecules dissociate to acetate form; then occurs an interaction of the acetate and the residual acid with the lattice OH of the clay at 200–300°C. This interaction involves the loss of the structural OH and deposition of carbon on the clay surfaces. The thermal decomposition of the residual complex is almost completed at 500–600°C
Kaolinite Synthesis. II. A Review and Discussion of the Factors Influencing the Rate Process
Authors: Van Oosterwyck-Gastuche M. C. , La Iglesia A.
Published: August 2006

Kaolinite is synthesized in approximately the same time in three temperature ranges: (1) from 200–250° to 350–400° (hydrothermal processes); (2) from 120 to 175° (semihydrothermal ones); (3) at ordinary temperature. It is thus evident that the rate process cannot be explained by the Arrhenius equation only, but is explained well by considering that kaolinite formation obeys the laws of crystal growth. It occurs only in slightly supersaturated solutions in which the nucleation process is possible and in which a slow and regular rate of growth has been insured. Concentrations calculated from the thermodynamical equilibria correspond to those of the experimental conditions for the low temperature processes. For the higher temperature ones, a similar relationship is delineated, at least as far as the thermodynamical treatment can be carried out.
Equilibration of Clays in Natural and Simulated Bottom-Sediment Environments
Authors: Photon F. E. , Smeck N. E.
Published: August 2006

To identify mineral alterations which might occur in stream environments, predominantly illitic soil clays were equilibrated in bottom sediment environments under natural and laboratory conditions for 217 and 98 days, respectively. Changes occurring after 217 days on the bottom of the Auglaize River, Ohio, consisted of a reduction in carbonate content, a decrease in particle size, and a slight loss of Al and Si; however, no significant changes in basal spacings were observed.

Clays equilibrated in river water under laboratory conditions at 4° and 25°C in CO2, N2, or air atmospheres showed only an increase in oxalate-extractable iron. The concentrations of Al, Si, Fe, Mn, K, and Ca in solution above the clays varied with the atmosphere and temperature. The concentrations of Fe, Al, and Si in solution may have been influenced by the dissolution of amorphous Al-Fe-Si compounds. Therefore, the mineralogical differences between soils in the watershed and sediments in the drainage system can not be attributed to mineralogical transformations during residence in the drainage system.
Stability of Parathion on Attapulgite as Affected by Structural and Hydration Changes
Authors: Gerstl Zev , Yaron Bruno
Published: August 2006

The structure and hydration status of attapulgite clay after heating at elevated temperatures and the stability of parathion on these clays was studied. Using infrared spectroscopy and scanning electron microscopy it was found that the bound water was lost in two steps, at 250° and 450° with the first step being largely reversible. At 650°C the structure began to dissolve releasing significant amounts of Mg, and a decrease in aggregate porosity was noted. At 850°C an amorphous phase was formed bearing little resemblance to the original attapulgite. Parathion was stable on all of the preheated clays when kept at 25°C for 190 days. The reactions of parathion on the preheated clays was studied at 110°C Hydrolysis of parathion was found to be minimal. Isomerization was the main reaction occurring on the Ca-attapulgite, whereas on an organo-clay no isomerization was observed. A mechanism for the isomerization reaction is proposed which entails a distortion of the phosphate moiety of the pesticide by the oxygen of the ligand water resulting in the conformational changes necessary for the isomerization to take place. On the organo-clay such a conformation was not possible; hence no isomerization occurred.
Synthesis and Properties of Poorly Crystalline Hydrated Aluminous Goethites
Authors: Fey Martin Venn , Dixon Joe Boris
Published: August 2006

Al-substituted goethites were prepared by rapid oxidation of mixed FeCl2-AlCl3 solutions at pH 6.8 in the presence of CO2 at 25°C. A combination of Al substitution and adsorption of CO2 reduced crystal size (except for an increase at small additions of Al) and produced unusual thin, porous particles. Product goethites had surface areas up to 283 m2/g and unit-cell expansions induced by hydration. Substitution of Al for Fe reduced the 111 spacing and increased infrared OH-bending vibrational frequencies. Al substitution split the goethite dehydroxylation endotherm during differential thermal analysis into a doublet and increased the temperature of all reactions. Both cold and hot alkali solutions dissolved Al from the goethite structure.

After drying the product in vacuo at 110°C. X-ray powder diffraction data indicated minimal deviation from Vegard's law for the goethite-diaspore solid solution up to about 30 mole % Al substitution. Goethite prepared in the presence of 40 mole % Al had a 111 spacing of 2.403 Å corresponding to 36 mole % structural Al if Vegard's law was obeyed. Rapid oxidation of mixed FeCl2-AlCl3 solutions appears to be conducive to a higher degree of Al substitution in goethite than alkaline aging of hydroxy-Fe(III)-Al coprecipitates.
Lithium and Potassium Saturation of Illite/Smectite Clays from Interlaminated Shales and Sandstones
Authors: Howard James J.
Published: August 2006

Mixed-layer illite/smectite (I/S) clays in lower Eocene sediments of the Texas Gulf Coast decrease in expandability with depth as found in previous studies of clay diagenesis, but at the same depth the 1/S clays from sand laminae tend to be more expandable than clays from adjacent shales. The I/S clays with greater expandability from sands collapse to phases with very low expandabilities after saturation with K. This non-ideal smectite behavior indicates that many of the expandable layers in I/S clays from sand laminae possess an illite-level negative layer charge on the structure. The Greene-Kelley Li-saturation test of the I/S clays also reveals that a considerable portion of the increased layer charge deficiency is created by tetrahedral substitution. The illitization of individual smectite layers in an I/S clay is envisioned to be a two step process instead of the single step rapid transformation implied in many earlier studies. The first rate-limiting step is the creation of sufficiently large negative layer charge in the lattice, primarily by AI for Si substitution in the tetrahedral sheet. The second rate-limiting step is the supply of K to the high-charged expandable layers. The abundance of high-charged expandable layers in I/S clays from sand laminae suggests that the K supply is influenced more by competing ions in the interstitial waters than by the absolute activity of K.
Grinding of Chrysotile in Hydrocarbons, Alcohol, and Water
Authors: Papirer Eugène , Roland Patrick
Published: August 2006

The change of the properties of chrysotile after ball milling in organic liquids (aromatics, alcohols, silicone oils) or water was studied by gas adsorption, electron microscopy, X-ray powder diffraction, infrared spectroscopy, differential thermal analysis, zeta potential measurements, and chemical analysis. Grinding in low viscosity organic solvents leads initially to a rapid defiberization of the asbestos bundles and to a fragmentation of the isolated fibrils. Finally, amorphization and agglomeration occur causing a drastic decrease of the specific surface area of the ground material. Grinding in water brings about a defiberization, but much more slowly than in organic solvents. Moreover, prolonged grinding in water does not significantly alter the structure of chrysotile. The efficiencies of the organic solvents, considered as grinding aids that induce fracture of the fibrils, are related to the environmental stress cracking of brittle solids (Rehbinder theory). Hence, the pertinent properties of the organic liquids are their viscosity and their cohesion energy (solubility parameter). Solvents chemisorbed on the surface of the ground chrysotile reduce the surface energy of the fracture surface and prevent aggregation. Water does not react according to Rehbinder's theory, but appears to form a protective layer around the fibrils. This hypothesis was verified by dry grinding defiberized asbestos (rapid amorphization) or by disturbing the stability of the water coating by coadsorbing alcohol on the solid surface. Alternatively, the resistance of the fibrils to fracture may be explained by Westwood's theory that grinding in water is equivalent to grinding in an alkali medium, wherein the surface charge of the chrysotile becomes negligible, and the mechanical stability of the fiber reaches a maximum.
Infrared Spectroscopy of Picloram Interactions with Al(III)-, Fe(III)-, and Cu(II)-Saturated and Hydrous Oxide-Coated Montmorillonite
Authors: Aochi Y. , Farmer W. J.
Published: August 2006

Thin clay films prepared from aqueous suspensions of the potassium or sodium salt of picloram (4-amino-3,5,6-trichloropicolinic acid) with Al-, Fe-, or Cu-saturated montmorillonite or with montmorillonite coated with hydrous oxides of Al, Fe, or Cu were examined in an air-dry condition by infrared (IR) techniques to elucidate possible modes of interaction between picloram and the mineral surfaces. Deuteration was used to confirm band assignments of picloram and its salts prior to interaction with montmorillonite. Picloram interactions with Al- and Fe-saturated montmorillonite and with montmorillonite coated with hydrous oxides of Al and Fe were concentration dependent. At high picloram concentrations similarities with the IR spectrum of potassium picloram indicated that much of the picloram was present in the salt form. As the concentration of picloram was reduced below that equivalent to 1 meq/g clay, the IR spectrum indicated the presence of the monomeric acid on the mineral surface. The spectrum of picloram on montmorillonite with a coating of copper hydrous oxide was similar to that of a Cu-picloram complex indicating coordination type bonding. The spectrum of picloram with Cu-saturated montmorillonite did not correspond to any of the other spectra of picloram examined. The interaction of picloram with montmorillonite coated with a hydrous oxide coating of Cu and with Cu-saturated montmorillonite were independent of picloram concentration in the range 2.20-0.44 meq/g clay.
Dissolution of Iron Oxides and Oxyhydroxides in Hydrochloric and Perchloric Acids
Authors: Sidhu P. S. , Gilkes R. J. , Cornell R. M. , Posner A. M. , Quirk J. P.
Published: August 2006

The dissolution of synthetic magnetite, maghemite, hematite, goethite, lepidocrocite, and akaganeite was faster in HCl than in HClO4. In the presence of H+, the Cl− ion increased the dissolution rate, but the ClO4− ion had no effect, suggesting that the formation of Fe-Cl surface complexes assists dissolution. The effect of temperature on the initial dissolution rate can be described by the Arrhenius equation, with dissolution rates in the order: lepidocrocite > magnetite > akaganeite > maghemite > hematite > goethite. Activation energies and frequency factors for these minerals are 20.0, 19.0, 16.0, 20.3, 20.9, 22.5 kcal/mole and 5.8 × 1011, 1.8 × 1010, 7.4 × 107, 5.1 × 1010, 2.1 × 1010, 3.0 × 1011 g Fe dissolved/m2/hr, respectively. The complete dissolution of magnetite, maghemite, hematite, and goethite is well described by the cube-root law, whereas that of lepidocrocite is not.
Hydrothermal Reactions of Clay Minerals and Shales with Cesium Phases from Spent Fuel Elements
Authors: Komarneni Sridhar , White William B.
Published: August 2006

The immobilization of soluble Cs from spent fuel elements by ion exchange and direct chemical reaction with clay minerals or shales was investigated under hydrothermal conditions. Various clay minerals or shales were reacted with likely Cs sources and water at 300 bars pressure and 100°, 200°, and 300°C for 4, 2, and 1 months, respectively. Pollucite was the principal product, but CsAlSiO4 was also observed, along with unreacted or hydrothermally altered aluminosilicates. From Cs concentrations of the product solutions partition of Cs between liquid and solids was found to vary depending on the Cs source, the clay or shale phase, temperature, and run duration. For example, illite-Cs2MoO4 interactions resulted in 19, 32, and 95% fixation of added Cs at 100°, 200°, and 300°C respectively. Fixation of as much as 97% of the Cs in some solids was observed. In addition to Cs-aluminosilicates, Cs was fixed on cation-exchange sites by interlayer collapse in montmorillonite. Reactions with Cs2MoO4 also produced powellite because Ca was available in the reaction mixture. The U6+ from β-Cs2U2O7 was reduced to form uraninite by sulfide- and/or organic-rich shales. (Cs,Na)2(UO2)(Si2O5)3·4H2O, an analog of weeksite, was produced in reactions with β-Cs2U2O7. The reaction products pollucite and uraninite can immobilize much of the Cs and U from spent fuel elements because Cs in pollucite is extremely difficult to exchange and U in uraninite is insoluble.
Zeolite Diagenesis Below Pahute Mesa, Nevada Test Site
Authors: Moncure George K. , Surdam Ronald C. , McKague H. Lawrence
Published: August 2006

The Tertiary silicic volcanic rocks in the Silent Canyon Caldera beneath Pahute Mesa, of the Department of Energy's Nevada Test Site have been divided into three vertical mineralogical zones that vary in thickness and transgress stratigraphic boundaries. Zonal contacts are generally sharp. Zone 1, the uppermost zone, includes unaltered or incipiently altered rhyolitic glass. Zone 2 is characterized by a predominance of clinoptilolite and subordinate amounts of smectite, cristobalite, and mordenite. Zone 3 is a complex mineral assemblage that includes analcime, quartz, calcite, authigenic K-feldspar and albite, kaolinite, chlorite, and mixed-layer illite/smectite. The mixed-layer clay shows an increase in ordering and a decrease in expandability with depth.

Shortly after deposition and after shallow burial, hydration of relatively impermeable, highly porous vitric rocks resulted in the rapid formation of the Zone 2 assemblage (except mordenite). This stage of alteration resulted in a net porosity loss and negligible mass transfer. Continued burial and rise in temperature led to a dehydration stage in which the Zone 2 assemblage was replaced by the Zone 3 minerals. The dehydration stage resulted in a porosity increase and an increase in permeability of several orders of magnitude. This process, like the earlier reactions, also conserved mass. Precipitation of mordenite followed the formation of this zonal configuration. The diagenetic zones below Pahute Mesa were caused by: (1) changing pore-water chemistry in an essentially closed hydrologic system; (2) disequilibrium or kinetic precipitation of metastable phases; and (3) a higher thermal gradient than that now present.
Electrical Conductivity and the Surface Characteristics of Kaolinitic Clays and Clay-Humic Acid Complexes
Authors: Lockhart N. C.
Published: August 2006

The conductivites of the Na and H ion-exchanged forms of kaolinitic clay rejects from sand-washing operations, both purified and as found naturally as a complex with soil organic matter, were examined. The two Na-clays showed linear conductivity-concentration characteristics, each having two regions with different slopes intersecting at ∼3.3% by weight of clay, which probably reflect a structural change from sol to gel. In the gel region, only the Na-counterions conducted, the reduction in conductivity with concentration being due to a smaller proportion of these ions in the Gouy layer and/or a decrease in their mobilities. In the sol, an additional, concentration-dependent conductivity arose from the electrophoretic motion of clusters of clay particles which gradually broke down on dilution. The two acid clays showed curved conductivity-concentration characteristics consistent with a weak acid dissociation equilibrium; the pKa values of 6.37 to 6.56 are close to those determined independently from titration with alkali. A stronger acid species detected in the titrations was not seen in the conductivity. The MOH2+/MOH/MO− model of the clay-surface species and one set of the predicted concentrations of each species (see preceding paper) are consistent with the observed conductivities. The MOH2+ species probably bridged the edges and faces of clay particles so that the H atoms were identical, but became different when alkali was added.