bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular and clinical analyses of 84 patients with tuberous sclerosis complex
Authors: Hung Chia-Cheng , Su Yi-Ning , Chien Shu-Chin , Liou Horng-Huei , Chen Chih-Chuan , Chen Pau-Chung , Hsieh Chia-Jung , Chen Chih-Ping , Lee Wang-Tso , Lin Win-Li , Lee Chien-Nan
Published: September 2006

Background

Tuberous sclerosis complex (TSC) is an autosomal dominant disease characterized by the development of multiple hamartomas in many internal organs. Mutations in either one of 2 genes, TSC1 and TSC2, have been attributed to the development of TSC. More than two-thirds of TSC patients are sporadic cases, and a wide variety of mutations in the coding region of the TSC1 and TSC2 genes have been reported.

Methods

Mutational analysis of TSC1 and TSC2 genes was performed in 84 Taiwanese TSC families using denaturing high-performance liquid chromatography (DHPLC) and direct sequencing.

Results

Mutations were identified in a total of 64 (76 %) cases, including 9 TSC1 mutations (7 sporadic and 2 familial cases) and 55 TSC2 mutations (47 sporadic and 8 familial cases). Thirty-one of the 64 mutations found have not been described previously. The phenotype association is consistent with findings from other large studies, showing that disease resulting from mutations to TSC1 is less severe than disease due to TSC2 mutation.

Conclusion

This study provides a representative picture of the distribution of mutations of the TSC1 and TSC2 genes in clinically ascertained TSC cases in the Taiwanese population. Although nearly half of the mutations identified were novel, the kinds and distribution of mutation were not different in this population compared to that seen in larger European and American studies.
What do you do for a living? Toward a more succinct definition of health services research
Authors: Phillips Charles D
Published: September 2006

This commentary discusses the need for, and the advantages of, a more concise, revised definition of the field of health services research. It argues for a definition that includes not only the topics on which health services research focuses but also the goals of health services research. A number of condensed definitions are provided for consideration.
Changes in aortic blood flow induced by passive leg raising predict fluid responsiveness in critically ill patients
Authors: Lafanechère A , Pène F , Goulenok C , Delahaye A , Mallet V , Choukroun G , Chiche JD , Mira JP , Cariou A
Published: September 2006

Introduction

Esophageal Doppler provides a continuous and non-invasive estimate of descending aortic blood flow (ABF) and corrected left ventricular ejection time (LVETc). Considering passive leg raising (PLR) as a reversible volume expansion (VE), we compared the relative abilities of PLR-induced ABF variations, LVETc and respiratory pulsed pressure variations (ΔPP) to predict fluid responsiveness.

Methods

We studied 22 critically ill patients in acute circulatory failure in the supine position, during PLR, back to the supine position and after two consecutive VEs of 250 ml of saline. Responders were defined by an increase in ABF induced by 500 ml VE of more than 15%.

Results

Ten patients were responders and 12 were non-responders. In responders, the increase in ABF induced by PLR was similar to that induced by a 250 ml VE (16% versus 20%; p = 0.15). A PLR-induced increase in ABF of more than 8% predicted fluid responsiveness with a sensitivity of 90% and a specificity of 83%. Corresponding positive and negative predictive values (PPV and NPV, respectively) were 82% and 91%, respectively. A ΔPP threshold value of 12% predicted fluid responsiveness with a sensitivity of 70% and a specificity of 92%. Corresponding PPV and NPV were 87% and 78%, respectively. A LVETc of 245 ms or less predicted fluid responsiveness with a sensitivity of 70%, and a specificity of 67%. Corresponding PPV and NPV were 60% and 66%, respectively.

Conclusion

The PLR-induced increase in ABF and a ΔPP of more than 12% offer similar predictive values in predicting fluid responsiveness. An isolated basal LVETc value is not a reliable criterion for predicting response to fluid loading.
The Circus in Ruins: A Comment on “Lion on Display: Culture, Nature, and Totality in a Circus Performance,” by Yoram Carmeli
Authors: Little Kenneth
Published: September 2006

This article comments on Yoram Carmeli's stimulating analysis of the narrative structure of Captain Sidney Howes's lion act performed in Gerry Cottle's British circus. I begin by discussing Carmeli's analysis of how the act functions socially and semiotically. According to him, this act plays on a formative underlying nature/culture structural opposition that is then subverted by circus culture only to be shown, in the end, to be part of the very bourgeois order it was supposed to challenge. I sketch out Carmeli's analysis of how the lions, Sidney Howes the trainer, and the circus itself serve as vehicles for a nostalgic spectacle of an exotic world that reformulates nature and culture into an even deeper message about the loss of originality as a discourse that conditions European modernity. My comments are meant to urge Carmeli to extend the work of nostalgia to the circus in ruins and the ever-present nightmare shadows of death, in the midst of dreamworld pleasure and titillation, which hovers over the circus. This means rethinking the role of representation and nostalgia which Carmeli finds underlying the lion act to see how the act, the artist Howes, and the circus may be understood alternatively as spectacle. My discussion ends with a suggestion about how the topic of death and ruins may open the possibility of another line of analysis, which tracks the twists and turns of circus spectacle as dreamworld and nightmare, now caught in the nervous system of postmodern capitalism, its tensions, oppositions, and contradictions.
Is a Public Reporting Approach Appropriate for Nursing Home Care?
Authors: Stevenson David G.
Published: September 2006

Publicizing quality information has been used as a quality improvement strategy in the acute care sector for more than a decade. Despite research showing mixed results of these efforts, publicly reporting quality measures is currently being pursued as a quality improvement strategy for nursing homes. Designed to empower consumers to make informed choices and to stimulate provider competition on quality, nursing home public reporting began in 1998 with the Nursing Home Compare Web site and has received greater emphasis in the 2002 Nursing Home Quality Initiative, both directed by the federal government. Focusing on the response of three key stakeholder groups across settings of care—consumers, providers, and purchasers—I identify several challenges that nursing home reporting must overcome to be successful. I conclude that publicly reporting quality measures for nursing homes will have a harder time promoting quality improvement than for acute care settings, where results have been disappointing thus far. In addition to the conceptual analysis, I evaluate whether the quality information reported on Nursing Home Compare had any impact on nursing home occupancy rates following its release. Using a pre/post-release design, I find that the effect of public reporting on nursing home occupancy rates has been minimal thus far. Although some estimates of effect are statistically significant and in the hypothesized direction, they all suggest very small effect sizes. It is unclear whether the absence of a larger reporting effect to date is specific to Nursing Home Compare or whether it inheres to the broader task of using quality information to promote change in the nursing home care sector.
Dynamin-related proteins Vps1p and Dnm1p control peroxisome abundance inSaccharomyces cerevisiae
Authors: Kuravi Kasinath , Nagotu Shirisha , Krikken Arjen M. , Sjollema Klaas , Deckers Markus , Erdmann Ralf , Veenhuis Marten , van der Klei Ida J.
Published: September 2006

Saccharomyces cerevisiae contains three dynamin-related-proteins, Vps1p, Dnm1p and Mgm1p. Previous data from glucose-grown VPS1 and DNM1 null mutants suggested that Vps1p, but not Dnm1p, plays a role in regulating peroxisome abundance. Here we show that deletion of DNM1 also results in reduction of peroxisome numbers. This was not observed in glucose-grown dnm1 cells, but was evident in cells grown in the presence of oleate. Similar observations were made in cells lacking Fis1p, a protein involved in Dnm1p function. Fluorescence microscopy of cells producing Dnm1-GFP or GFP-Fis1p demonstrated that both proteins had a dual localization on mitochondria and peroxisomes. Quantitative analysis revealed a greater reduction in peroxisome number in oleate-induced vps1 cells relative to dnm1 or fis1 cells. A significant fraction of oleate-induced vps1 cells still contained two or more peroxisomes. Conversely, almost all cells of a dnm1 vps1 double-deletion strain contained only one, enlarged peroxisome. This suggests that deletion of DNM1 reinforces the vps1 peroxisome phenotype. Time-lapse imaging indicated that during budding of dnm1 vps1 cells, the single peroxisome present in the mother cell formed long protrusions into the developing bud. This organelle divided at a very late stage of the budding process, possibly during cytokinesis.
Locomotion byAbdopus aculeatus(Cephalopoda: Octopodidae):walking the line between primary and secondary defenses
Authors: Huffard Christine L.
Published: September 2006

Speeds and variation in body form during crawling, bipedal walking,swimming and jetting by the shallow-water octopus Abdopus aculeatuswere compared to explore possible interactions between defense behaviors and biomechanics of these multi-limbed organisms. General body postures and patterns were more complex and varied during the slow mode of crawling than during fast escape maneuvers such as swimming and jetting. These results may reflect a trade-off between predator deception and speed, or simply a need to reduce drag during jet-propelled locomotion. Octopuses swam faster when dorsoventrally compressed, a form that may generate lift, than when swimming in the head-raised posture. Bipedal locomotion proceeded as fast as swimming and can be considered a form of fast escape (secondary defense) that also incorporates elements of crypsis and polyphenism (primary defenses). Body postures during walking suggested the use of both static and dynamic stability. Absolute speed was not correlated with body mass in any mode. Based on these findings the implications for defense behaviors such as escape from predation, aggression, and `flatfish mimicry' performed by A. aculeatus and other octopuses are discussed.
Centre of mass movement and mechanical energy fluctuation during gallop locomotion in the Thoroughbred racehorse
Authors: Pfau Thilo , Witte Thomas H. , Wilson Alan M.
Published: September 2006

During locomotion cyclical interchange between different forms of mechanical energy enhances economy; however, 100% efficiency cannot be achieved and ultimately some mechanical work must be performed de novo. There is a metabolic cost associated with fluctuations in mechanical energy, even in the most efficient animals. In this study we investigate the exchanges between different forms of mechanical energy involved in high-speed gallop locomotion in Thoroughbred race horses during over-ground locomotion using innovative, mobile data collection techniques. We use hoof-mounted accelerometers to capture foot contact times, a GPS data logger to monitor speed and an inertial sensor mounted over the dorsal spinous processes of the fourth to sixth thoracic vertebrae (the withers) of the horse to capture trunk movement with six degrees of freedom. Trunk movement data were used to estimate the movement of the centre of mass (CoM). Linear(craniocaudal, mediolateral and dorsoventral) and rotational (roll, pitch and heading) kinematic parameters (displacement, velocity and acceleration) were calculated for seven horses at gallop speeds ranging from 7 to 17 m s-1 during their regular training sessions. These were used to estimate external mechanical energy (potential energy and linear kinetic energy of the CoM) as well as selected components of internal energy (angular kinetic energy). Elastic energy storage in the limbs was estimated from duty factor, sine wave assumptions and published leg stiffness values.

External mechanical energy changes were dominated by changes in craniocaudal velocity. Potential energy change, which was in phase with craniocaudal energy during the front limb stances, was small. Elastic energy storage in the limbs was small compared to the overall amplitude of fluctuation of external mechanical energy. Galloping at high speeds does not therefore fit classical spring mass mechanics.
The locomotor kinematics of Asian and African elephants: changes with speed and size
Authors: Hutchinson John R. , Schwerda Delf , Famini Daniel J. , Dale Robert H. I. , Fischer Martin S. , Kram Rodger
Published: September 2006

For centuries, elephant locomotion has been a contentious and confusing challenge for locomotion scientists to understand, not only because of technical difficulties but also because elephant locomotion is in some ways atypical of more familiar quadrupedal gaits. We analyzed the locomotor kinematics of over 2400 strides from 14 African and 48 Asian elephant individuals (body mass 116-4632 kg) freely moving over ground at a 17-fold range of speeds, from slow walking at 0.40 m s-1 to the fastest reliably recorded speed for elephants, 6.8 m s-1. These data reveal that African and Asian elephants have some subtle differences in how size-independent kinematic parameters change with speed. Although elephants use a lateral sequence footfall pattern, like many other quadrupeds, they maintain this footfall pattern at all speeds, shifting toward a 25% phase offset between limbs (singlefoot) as they increase speed. The duty factors of elephants are greater for the forelimbs than for the hindlimbs, so an aerial phase for the hindquarters is reached at slower speeds than for the forequarters. This aerial phase occurs at a Froude number of around 1,matching theoretical predictions. At faster speeds, stance and swing phase durations approach asymptotes, with the duty factor beginning to level off,concurrent with an increase in limb compliance that likely keeps peak forces relatively low. This increase of limb compliance is reflected by increased compression of the hindlimbs. Like other tetrapods, smaller elephants are relatively more athletic than larger ones, but still move very similarly to adults even at <500 kg. At any particular speed they adopt greater relative stride frequencies and relative stride lengths compared to larger elephants. This extends to near-maximal locomotor performance as well - smaller elephants reach greater Froude numbers and smaller duty factors, hence likely reach relatively greater peak loads on their limbs and produce this force more rapidly. A variety of lines of kinematic evidence support the inference that elephants change their mechanics near a Froude number of 1 (if not at slower speeds), at least to using more compliant limbs, if not spring-like whole-body kinetics. In some ways, elephants move similarly to many other quadrupeds,such as increasing speed mainly by increasing stride frequency (except at fast speeds), and they match scaling predictions for many stride parameters. The main difference from most other animals is that elephants never change their footfall pattern to a gait that uses a whole-body aerial phase. Our large dataset establishes what the normal kinematics of elephant locomotion are, and can also be applied to identify gait abnormalities that may signal musculoskeletal pathologies, a matter of great importance to keepers of captive elephants.
Wing beat kinematics of a nectar-feeding bat,Glossophaga soricina,flying at different flight speeds and Strouhal numbers
Authors: Norberg Ulla M. Lindhe , Winter York
Published: September 2006

High-speed film analysis showed that the wing beat kinematics in Glossophaga soricina change gradually with increasing flight speed,indicating that there is no sudden gait change at any particular, critical,flight speed. The flight of two adult specimens was studied over a range of flight speeds (1.23-7.52 ms-1) in a 30 m long flight tunnel. During the upstroke in hovering and slow flight there is a tip-reversal or supination of the handwings, which thus produce a backward flick. This backward motion successively disappears at speeds V≈3.2 ms-1, above which the wingtip path becomes more vertical or directed upwards-forwards relative to the still air (the stroke plane angle increasing with flight speed as α=44.8V0.29). We found no correlations between either span ratio SR (the ratio of the wing span on the upstroke to that on the downstroke) and V, or downstroke ratio (the duration of the downstroke divided by the total stroke period) and V.On the other hand, SR decreases significantly with increasing wing beat frequency f, SR∝f-0.40. The Strouhal number (St=f×amplitude/V), a dimensionless parameter describing oscillating flow mechanisms and being a predictor of the unsteadiness of the flow, decreases with the speed as St∝V-1.37. Close to the theoretical minimum power speed (4-6 m s-1) G. soricina operates with a Strouhal number in the region 0.17<St<0.22, which is associated with efficient lift and thrust production. At slower speeds, 3.4-4 m s-1, St is 0.25-0.4, which is still within the favourable region. But at speeds below 3 m s-1St becomes higher(0.5<St<0.68), indicating that unsteady effects become important, with unfavourable lift and thrust production as a result. Only at these speeds do the bats perform the backward flick during the upstroke, which may produce thrust. This may serve as a compensation in some bats and birds to increase aerodynamic performance.
Laboratory behavioural assay of insect magnetoreception:magnetosensitivity of Periplaneta americana
Authors: Vácha Martin
Published: September 2006

A relatively simple all-laboratory behavioural assay of insect magnetoreception has been developed. We found non-conditioned reactions of American cockroach to the periodical shifts of the geomagnetic field. The movement activity of animals individually placed into Petri dishes was scored as a number of body turns. Test groups were exposed to a 90-min interval with the horizontal component of the geomagnetic field periodically rotated by 60° back and forth with 5 min periodicity. The number of body turns was compared with the preceding and following intervals and with the corresponding interval of the control group kept in the natural field. We obtained a significant increase in activity when changes in field were applied. Interestingly, the period of increased activity did not coincide precisely with the 90 min stimulation interval. The onset of animal restlessness was delayed by tens of minutes and persisted correspondingly after the stimulation stopped. A respective evaluation criterion was suggested and verified.

Owing to its simplicity and minimal manipulation of the insects, together with low demands on the memory and motivation state of animals, the approach potentially may be used as a laboratory diagnostic tool indicating magnetoreception in insect neurophysiology research.
An RNA ligase-mediated method for the efficient creation of large, synthetic RNAs
Authors: Stark Martha R. , Pleiss Jeffrey A. , Deras Michael , Scaringe Stephen A. , Rader Stephen D.
Published: September 2006

RNA ligation has been a powerful tool for incorporation of cross-linkers and nonnatural nucleotides into internal positions of RNA molecules. The most widely used method for template-directed RNA ligation uses DNA ligase and a DNA splint. While this method has been used successfully for many years, it suffers from a number of drawbacks, principally, slow and inefficient product formation and slow product release, resulting in a requirement for large quantities of enzyme. We describe an alternative technique catalyzed by T4 RNA ligase instead of DNA ligase. Using a splint design that allows the ligation junction to mimic the natural substrate of RNA ligase, we demonstrate several ligation reactions that appear to go nearly to completion. Furthermore, the reactions generally go to completion within 30 min. We present data evaluating the relative importance of various parameters in this reaction. Finally, we show the utility of this method by generating a 128-nucleotide pre-mRNA from three synthetic oligoribonucleotides. The ability to ligate synthetic or in vitro transcribed RNA with high efficiency has the potential to open up areas of RNA biology to new functional and biophysical investigation. In particular, we anticipate that site-specific incorporation of fluorescent dyes into large RNA molecules will yield a wealth of new information on RNA structure and function.
Infrared Spectroscopic Study of Adsorbed Water on Reduced-Charge Na/Li-Montmorillonites
Authors: Sposito Garrison , Prost R. , Gaultier J.-P.
Published: September 2006

Infrared (IR) spectra in the fundamental and near-IR regions were obtained for Na-saturated Wyoming montmorillonite and reduced-charge Na/Li-saturated Wyoming montmorillonites hydrated under water vapor at 50% RH and dehydrated under vacuum. For the Na-montmorillonite, changes in the intensities of the structural OH-bending modes, particularly that of the MgAlOH group, were observed as the clay was dehydrated. This result was interpreted as evidence that exchangeable Na ions lose solvation water and settle into the ditrigonal cavities on the clay surface as it becomes desiccated. For the Na/Li-montmorillonites, the structural OH-bending modes also decreased in IR intensity because of Li+ migration into the octahedral sheet. The fundamental IR spectra of D2O adsorbed by the montmorillonites showed characteristic absorptions at 2685, 2510, 2400, and 1205 cm-1 that decreased in intensity proportionally to the cation-exchange capacity. This result, along with corroborating data from X-ray powder diffractograms and from near-IR diffuse reflectance spectra of H2O adsorbed by the clays, suggest that the exchangeable cations on Na-montmorillonite dissociated from the clay surface as it hydrated and played a significant role in organizing the structure of adsorbed water at low water contents.
Infrared Spectra of Thiolane and Tetramethylene Sulfoxide Adsorbed on Montmorillonite
Authors: Lorprayoon V. , Condrate R. A.
Published: September 2006

Infrared spectra (4000-1200 cm-1) were obtained for several homoionic montmorillonite films on which tetramethylene sulfoxide (TMSO) or thiolane were adsorbed at various temperatures and for different periods of exposure. The spectra indicate that the Na-, H-, and natural montmorillonite complexes contain a physically adsorbed species, whereas transition metal-montmorillonite complexes contain both physically adsorbed and metal-complexed species in their interlamellar spaces. Apparently, thiolane adsorbed on most montmorillonites undergoes oxidation to TMSO in an air atmosphere. Consistent with the mechanism proposed earlier for aqueous solutions, the rate of sulfoxide formation increases by increasing the pH of the suspensions from which the clay films were deposited or by increasing the concentration of the water molecules in the interlamellar spaces. The infrared spectra of γ-thiolactone adsorbed on Co-montmorillonites suggest that sulfoxide-type molecules are formed which chelate to the Co ions in the interlamellar spaces.
Apparent Charge Heterogeneity in Kaolins in Relation to Their 2:1 Phyllosilicate Content
Authors: Talibudeen Oscar , Goulding Keith W. T.
Published: September 2006

Measurements of the differential heats of K-Ca exchange are used to show that 6 groups of sites (ranging from −13.8 to −5.1 kJ/eq and with as many as 4 in any one sample) exist in kaolins that range from 0 to 15% in their 2:1 phyllosillicate content. These heat values, coupled with entropies of exchange, suggest that 0.1−10% vermiculitic, micaceous, and smectitic layers are present, presumably interstratified with kaolinitic layers which are assumed to have no permanent charge. Changes in the activity coefficients of adsorbed K with K saturation confirm these conclusions qualitatively. Thus, fK values at x ↑ 0 correlate inversely (r2 = 0.655) with the content of vermiculite + partially expanding micas, and x values at maximum fK indicate the content of vermiculite + nonexpanding mica + partially expanding micas (r2 = 0.732).
Thermal Transformation of Antigorite as Studied by Electron-Optical Methods
Authors: Santos Helena de Souza , Yada Keiji
Published: September 2006

The thermal transformation of a Brazilian antigorite heated dry from 600° to 1300°C, was studied by high resolution electron microscopy and selected area electron diffraction (SAD). Below 600°C, the antigorite particles did not change morphologically or crystallographically, as evidence by the presence of the superlattice in the SAD patterns and lattice images. At 650°C, traces of antigorite remained, although the superlattice structure had disappeared and the first indications of forsterite formation were observed in the same SAD. Diffraction patterns of the transition phases showed various topotactical relationships between antigorite and forsterite. At 800°C, the crystallization to forsterite was much more pronounced. At 900°C, the individual particles retained their original shapes, but they were actually pseudomorphs, for their SAD patterns showed only forsterite. Between 1000° and 1300°C various topotactical relationships were observed. Although the overall transformation to forsterite appears to be similar for both chrysotile and antigorite, the transformation of antigorite took place at a slightly higher temperature (~50°C) with a larger number of topotactical relationships than for chrysotile. Enstatite was formed at 1300°C, but it was impossible to determine the topotactic relations between enstatite and forsterite, which was possible with chrysotile.
Noncentric Layer Silicates: An Optical Second Harmonic Generation, Chemical, and X-Ray Study
Authors: Guggenheim Stephen , Schulze Walter A. , Harris Gene A. , Lin Jiunn-Chorng
Published: September 2006

Twenty-nine chlorites, seventeen lithium-free micas, and twenty-two lithium-bearing micas from diverse localities have been studied by X-ray diffraction, microprobe, and optical second harmonic generation (SHG) techniques to determine which are noncentric and the cause of acentricity. Manandonite (B-rich chlorite) and cookeite, both crystallizing in the Ia form, are acentric. Sudoite-IIb gave a questionable SHG signal, possibly indicating acentricity. All other chlorites gave null signals. Bityite, a Li, Be mica similar to margarite, was determined from the positive SHG response to be acentric. It crystallizes in the 2M1 form and, by analogy to margarite, is ordered tetrahedrally in subgroup symmetry, Cc. Masutomilite-1M and “cryophyllite“-1M (a zinnwaldite high in Al and Si, but low in Fe) are acentric and most probably crystallize in space group C2, thus allowing a noncentric octahedral ordering pattern. Lepidolites showed a diversity in SHG response with only a few being acentric; a lepidolite-1M from Mesagrande, California, a lepidolite-3T from Windhuk, South West Africa, and a lepidolite-2M2 from Nagatare, Japan, gave positive SHG responses. The Japanese material is complexly intergrown and twinned, and intergrain reflection or refraction may have produced spurious signals.

Most lithium-free micas showed diversity in SHG response and, although most were non-emitters, clintonite from Amity, New York, showed a positive response, but this sample is twinned and shows stacking disorder. A “manganophyllite”-1M (manganoan phlogopite) from Langban, Sweden, showed a very weak positive response; however, the presence of Mn alone is not suffcient to produce octahedral cation ordering in noncentric subgroup symmetry. Two manganoan phlogopites from Japan were refined in subgroup symmetry, and the higher order and ideal symmetry of C2/m was confirmed.
Surface Properties of Smectites Exchanged with Mono- and Biprotonated 1,4-Diazobicyclo(2,2,2)-Octane
Authors: Van Leemput L. , Stul M. S. , Maes A. , Uytterhoeven J. B. , Cremers A.
Published: September 2006

Smectites exchanged to various degrees with mono- or biprotonated 1,4-diazobicyclo(2,2,2)-octane (Dabco) have a porous structure in which the organic molecule acts as a “pillar.” Less Dabco2+ than Dabco1+ was necessary both to initiate and to complete expansion, whereas for both Dabco1+ and Dabco2+ the threshold for expansion increased with the charge density of the clay. Interstratification of 9.7-Å and 14.5-Å (Dabco1+) or 14.1-Å (Dabco2+) layers was observed before full expansion occurred.

Nitrogen sorption isotherms on partially exchanged Dabco1+- and Dabco2+-clays are of the BET II and Langmuir type respectively, whereas n-butane adsorbed according to BET type II for both cationic forms. The specific surface area was governed by the number of Dabcoz+ pillars, irrespective of the inorganic cation, and increased with Dabcoz+ content even beyond the composition where full expansion was reached and notwithstanding the increasing number of silicate layers in the c direction of the crystal units. This relationship is explained by an enhanced random interleaving of clay platelets in the stacking units containing Dabcoz+.
Effect of pH on the Formation of Goethite and Hematite from Ferrihydrite
Authors: Schwertmann U. , Murad E.
Published: September 2006

Storage of ferrihydrite in aqueous suspensions at 24°C and pHs between 2.5 and 12 for as long as three years resulted in the formation of goethite and hematite. The proportions and crystallinity of these products varied widely with the pH. Maximum hematite was formed between pH 7 and 8, and maximum goethite at pH 4 and at pH 12. The crystallinity of both products, as indicated by X-ray powder diffraction line broadening and magnetic hyperfine field values and distribution widths, was poorer, the lower the proportion of the corresponding product in the mixture. The existence of two competitive formation processes is suggested: goethite is formed via solution, preferably from monovalent Fe(III) ions [Fe(OH)2+ and Fe(OH)4−], and hematite by internal rearrangement and dehydration within the ferrihydrite aggregates. This concept relates the proportions of goethite and hematite to the activity of the Fe(III) ion species in solution, and implies that conditions favorable for the formation of goethite are unfavorable for that of hematite and vice versa.
Anion-Exchange Properties of Hydrotalcite-Like Compounds
Authors: Miyata Shigeo
Published: September 2006

Ion-exchange isotherms between hydrotalcite-like compounds (HT) of the NO3-, Cl-, and SO4- forms and F−, Cl− Br−, I−, OH−, SO42−, CO32−, and Naphthol Yellow S (NYS2−) ions were determined, and the spacing and the width of the 003 reflection were measured as a function of HT composition. The ion-exchange equilibrium constant for HTs of monovalent anions are in the sequence OH− > F− > Cl− > Br− > NO3− > I−, those for divalent anions are in the sequence CO32− > NYS2− > SO42−. The ion-exchange equilibrium constants tend to increase as the diameters of the anions decrease, and the crystallite size in the 001 direction tends to increase with anions having higher selectivity. The OH-form of HT has the smallest basal spacing and the largest crystallite size in the 001 direction.
Hydrogen Atom Positions in Kaolinite by Neutron Profile Refinement
Authors: Adams J. M.
Published: September 2006

A structure refinement of kaolinite made using the Rietveld neutron profile refinement technique has given non-hydrogen atom positions which were not significantly different from those given by B. B. Zvyagin in 1960. All of the hydrogen atoms have been located; the three inner-surface hydrogen atoms are involved in interlayer hydrogen bonds with lengths of 2.95(4), 2.95(4), and 3.06(4) Å with O-H ... O angles of 168(4)°, 144(4)°, and 146(4)° respectively. The inner hydrogen atom is located in a position consistent with that found earlier in dickite and muscovite which are the only dioctahedral layer silicates studied by neutron diffraction to date. The O-H vector makes an angle of 34° with the (001) plane, away from the octahedral sheet, and the projection of the vector on to (001) is at ~30° to the b axis.
Extended Version of Gouy-Chapman Electrostatic Theory as Applied to the Exchange Behavior of Clay in Natural Waters
Authors: Neal C. , Cooper D. M.
Published: September 2006

A model based on Gouy-Chapman theory, describing the ion exchange behavior of clays in mixed electrolyte solutions is presented. Computed ionic distributions, taking into account variations in relative permittivity, ion activity, and closeness of approach of ions to clay surfaces, are compared with experimental data for smectite and kaolinite in contact with river and saline waters. To obtain reasonable agreement between theoretical prediction and observation the most important extension of Gouy-Chapman theory involves the introduction of a closeness of approach term. Furthermore, the aggregated nature of smectites plays an important part in controlling its exchange properties, whereas a fixed-charge model provides a poor description for the ion exchange properties of kaolinite.
Dehydroxylation, Rehydroxylation, and Stability of Kaolinite
Authors: Hurst Vernon J. , Kunkle Albert C.
Published: September 2006

From hydrothermal experiments three pressure-temperature-time curves have been refined for the system Al2O3−SiO2−H2O and reversal temperatures established for two of the principal reactions involving kaolinite. The temperatures of three isobaric invariant points enable the Gibbs free energy of formation of diaspore and pyrophyllite to be refined and the stability field of kaolinite to be calculated. The maximal temperature of stable kaolinite decreases from 296°C at 2 kb water pressure to 284°C at water's liquid/vapor pressure, and decreases rapidly at lower pressures. On an isobaric plot of [H4SiO4] vs. °K-1, kaolinite has a wedge-shaped stability field which broadens toward lower temperature to include much of the [H4SiO4] range of near-surface environments. If [H4SiO4] is above kaolinite's stability field and the temperature is < 100°C, halloysite forms rather than pyrophyllite, an uncommon pedogenic mineral. Pyrophyllite forms readily instead of kaolinite above 150°C if [H4SiO4] is controlled by cristobalite or noncrystalline silica.

Kaolinite and a common precursor, halloysite, are characteristic products of weathering and hydro-thermal alteration. In sediments, relatively little halloysite has survived due to its low dehydration temperature and instability at low water pressure, but kaolinite commonly has survived since the Devonian Period. In buried sediments, the water pressure and [H4SiO4] requisite for stable kaolinite generally are maintained. In oxidized sediments and in pyritic reduced sediments, kaolinite commonly has survived, but where alkalies, alkaline earths, or aqueous iron has concentrated in the pore fluid, kaolinite has tended to transform to illite, zeolites, berthierine, or other minerals.
Iron Sites in Nontronite and the Effect of Interlayer Cations from Mössbauer Spectra
Authors: Johnston J. H. , Cardile C. M.
Published: September 2006

The 57Fe Mössbauer spectra of untreated, Ca- and K-saturated nontronite from Garfield, Washington, were measured. The spectrum of the untreated sample was computer-fitted to 8 peaks defining two octahedral, a tetrahedral, and an interlayer Fe3+-quadrupole-split doublets. In the Ca- and K-saturated samples interlayer Fe was absent. Spectra of the untreated sample were recorded at increasing increments of background counts from 2.8 × 105 to 9.2 × 106. An evaluation of the initial 4- and 6-peak models and the acceptable 8-peak model, computer-fitted to each spectrum, shows that if the χ2 value is used as a measure of the goodness of the fit, the spectra should be recorded to a background count greater than 3 × 106. The resulting χ2 value then reflects both the validity of the model used and the extent of disorder within the structure. The χ2 value depends linearly on the background counts obtained.

A comparison of the spectra of the Ca- and K-saturated samples with that of the untreated sample shows that the interlayer cations exert a considerable influence on the individual component resonances, particularly the outer octahedral doublet. Hence, it is likely that electrostatic interactions of the nearby tetrahedral Fe3+ and the interlayer cations give rise to two distinct electric field gradients within neighboring cis-[FeO4(OH)2] sites, and hence two octahedral Fe3+ doublets in the Mössbauer spectrum. These results are consistent with earlier electron diffraction data in the literature.
Electromobility of Mica Particles Dispersed in Aqueous Solutions
Authors: Pashley R. M.
Published: September 2006

Mobility measurements were made for dry-ground mica particles dispersed in aqueous KCl, Cr(NO3)3, and cetyltrimethylammonium bromide (CTAB) solutions. In the latter solutions charge reversal occurred at about 2 × 10-6 M and 3 × 10-5 M, respectively. Negative zeta potentials in KCl solutions calculated using the Smoluchowski equation are about one third of the corresponding values obtained from streaming potentials and force measurements using mica sheets. Good agreement, however, was obtained when positively charged groups created during grinding were neutralized, and the zeta potentials were corrected according to the procedure of O'Brien and White with an assumed average particle size of 0.25 μm. When the zeta potentials of positively charged particles were corrected in this way, agreement with values calculated from force measurements was also improved.
Small-Angle X-Ray Powder Diffraction, Morphology, and Structure of Allophane and Imogolite
Authors: van der Gaast S. J. , Wada K. , Wada S.-I. , Kakuto Y.
Published: September 2006

Small-angle X-ray powder diffraction analyses and high-resolution electron microscopy of allophane samples (SiO2/Al2O3 ratio, 1.12 to 1.68) showed that allophanes consist of nearly identical spherical particles with diameters of about 40 Å and retain their characteristic “hollow” spherical morphology at different ambient moisture and even after dehydroxylation by heating at 500° to 600°C. Unheated allophane samples gave another X-ray powder diffraction band whose maximum position varied from 12.3 to 14.5 A depending on their SiO2/Al2O3 ratio. The appearance of this band may denote some long-range ordering in the structure of allophane. Unlike the spherical particles of allophane, the tube unit of imogolite collapsed on dehydroxylation. This observation suggests that imogolite and allophane are different in their framework structures and that a Si- or Si(Al)-tetrahedral sheet rather than an Al-octahedral sheet constitutes the framework structure of allophane, irrespective of its SiO2/Al2O3 ratio.
Structural Studies of Nontronites with Different Iron Contents by 57Fe Mössbauer Spectroscopy
Authors: Cardile C. M. , Johnston J. H.
Published: September 2006

The 57Fe Mössbauer spectra of a series of untreated and Ca-saturated nontronites showed a predominant Fe3+ resonance which was computer-fitted with two Fe3+ doublets defining iron in non-equivalent cis-FeO4(OH)2 octahedral sites. In most spectra a doublet indicating tetrahedral Fe3+ was fitted and in one untreated sample a doublet indicating interlayer Fe3+ was identified. In a further untreated sample the interlayer iron was present as Fe2+. Upon Ca-saturation the interlayer iron was displaced. It also appears that the interlayer iron was present in at least two different interlayer sites. From the computer-fitted data it was clear that the interlayer cations have a significant effect on the Mössbauer resonances of iron in the two non-equivalent cis-octahedral and the tetrahedral sites of nontronite.
Mechanism of Synthesis of 10-Å Hydrated Kaolinite
Authors: Raythatha Rasik , Lipsicas Max
Published: September 2006

The synthesis of 10-Å hydrated kaolinite was accomplished by: (1) direct reaction of HF with a dimethyl sulfoxide (DMSO)-kaolinite intercalate and water washing; (2) methanol washing of a DMSO-kaolinite intercalate followed by reaction with any alkali fluoride salt and water washing; and (3) room-temperature (RT) water-washing of a methanol-washed DMSO-kaolinite intercalate. In all syntheses the optimum yield required a kaolinite in which DMSO was bound strongly to the interlayer surface. In the first synthesis, water inclusion between clay layers appeared to be facilitated by the reduction of cohesive interlayer forces brought about by replacement of surface and edge OH− by F−. The fluorination reaction was accomplished either by direct reaction of HF or by HF produced through the hydrolysis of NH4F at 60°C. In the second synthesis, intercalated DMSO was replaced by methanol. F− solvated readily in methanol but not in DMSO. Consequently, F− produced through hydrolysis of the alkali fluoride salt entered the interlayer space and contributed to the fluorination reaction. Furthermore, the diffusion of methanol out of the interlayer space during the RT-washing step was slowed by F≈ solvation which aided the exchange of methanol for water. High yields of 10-Å kaolinite hydrate were obtained irrespective of choice of alkali fluoride salt. The third synthesis was dependent on matching the diffusion of methanol out of the interlayer space with diffusion of water into this space. At room temperature the diffusion rates were close enough to maintain the clay in the expanded state throughout the hydration process, and high yields of 10-Å kaolinite hydrate were obtained. At 60°C the diffusion rates were too dissimilar, and very low yields of hydrate were obtained.
Size Distribution of Allophane Unit Particles in Aqueous Suspensions
Authors: Hall P. L. , Churchman G. J. , Theng B. K. G.
Published: September 2006

The size distribution of unit particles of two New Zealand allophanes (An and Rh), in dilute (0.8% w/v) aqueous suspensions, has been determined by small-angle neutron scattering (SANS). In addition, the specific surface area of the samples was measured by ethylene glycol retention, and their morphology examined by high-resolution transmission electron microscopy (HRTEM). The SANS data indicate that although both allophanes are somewhat polydisperse, the average diameter of their unit particles is significantly different, being 56 and 43 Å for allophane-An and allophane-Rh, respectively. Consistent with this observation, the specific surface area of allophane-Rh (897 mVg) is appreciably greater than that of allophane-An (638 m2/g). Under the electron microscope, both samples appear as aggregates of hollow spherules but HRTEM did not clearly distinguish between the two allophanes in that the largest population of spherules had diameters near 50 Å. Because of the assumptions and uncertainties involved in the SANS and surface area measurements, the data must be discussed in terms of their respective ratios. On this basis, the spherule diameter ratio is of the same order of magnitude as the inverse ratio of specific surface area. The latter value is also in reasonably good agreement with the corresponding ratios of phosphate adsorption capacity and BET nitrogen areas, derived from earlier studies.
Hydration States of Interlamellar Chromium Ions in Montmorillonite
Authors: Carr R. Melville
Published: September 2006

Hydroxychromium montmorillonites were prepared from solutions containing chromium nitrate and varying amounts of NaOH. The reactant Cr ions were hydrolyzed and, in some experiments, were dimerized to a significant extent. The extent of polymerization in the product formed from a solution containing a maximum amount of [Cr2(H2O)8(OH)2]4+ was compared with that in products obtained from solutions containing monomer, [Cr(H2O)5OH]2+, and lesser amounts of the dimer. Despite the uncertainty about the nature and amounts of product interlamellar species, the catalytic effect of the montmorillonite interlayer on the hydrolysis and polymerization of Cr(III) appears to be independent of the nature of the reactant species. The validity of this conclusion depends to a large extent on the reliability of water determination in the clay mineral species, which is estimated to be no better than 5%. The assumption that H2O+ is 'combined’ and H2O— is 'free’ water is shown to be partially true, thereby causing some uncertainty in the interpretations of interlayer compositions.
Properties of Goethites of Varying Crystallinity
Authors: Schwertmann Udo , Cambier Philippe , Murad Enver
Published: September 2006

Goethites were synthesized from ferrihydrite in 0.7 M KOH between 4° and 90°C. As temperatures increased, the goethite crystals became larger and of less domainic character, and surface areas decreased from 153 to 9 m2/g. Surface area, oxalate-soluble Fe to total Fe ratios, chemisorbed water, Mössbauer parameters, and dissolution rate in 6 M HCl at 25°C are particle-size controlled, whereas mean crystallite dimensions, a-dimension of the unit cell, differences between the two OH-bending modes, and dehydroxylation temperatures suggest the existence of a low-temperature (high-a-dimension) and a high-temperature (low-a-dimension) goethite, with a narrow transition range at a synthesis temperature of 40°–50°C. Hydrothermal treatment at 125°–180°C of a low-temperature goethite led to a healing of the multidomainic, microporous high-a-dimension goethite into a monodomainic low-a-dimension goethite of similar overall crystal size with the properties of a low-a-dimension goethite.
Effect of Clay Mineralogy and Aluminum and Iron Oxides on the Hydraulic Conductivity of Clay-Sand Mixtures
Authors: Alperovitch N. , Shainberg I. , Keren R. , Singer M. J.
Published: September 2006

Changes in hydraulic conductivity and clay dispersivity of clay-sand mixtures (four reference smectites and Fithian illite) as a function of concentration (0.01 M Cl− and distilled water) and sodium adsorption ratio (SAR ≤ 30) of the percolating solution were measured. In addition, the effect of sand percentage, sand particle size, and addition of AlCl3 and FeCl3 on the hydraulic conductivity of the mixtures were measured.

Clay dispersion and migration out of the 3% clay columns was substantial. The clay dispersed only in the distilled water system; dispersion increased with an increase in the percentage of exchangeable Na and was about the same for the Wyoming montmorillonite and Fithian illite. Conversely, the clay swelled in the 0.01 M Cl− solution. The swelling of the montmorillonites increased in the order: Upton, Wyoming = Belle Fourche, South Dakota > Polkville, Mississippi > Otay, California, and was higher than that of the Fithian illite. The swelling and dispersion of the clay accounted for the changes in hydraulic conductivity.

Mixtures treated with FeCl3 and AlCl3 were leached with NaCl-CaCl2 solutions until the pH of the effluent exceeded 6.5. The composition of the exchangeable phase was then determined by the SAR of the leach solutions. At pH > 6.5, the polycations hydrolyzed and were present as the hydroxy-polymer species. The hydraulic conductivity of the mixtures decreased as exchangeable Na increased, but the decrease was less than in untreated mixtures, AlCl3 was more effective in maintaining hydraulic conductivity than FeCl3. In montmorillonite clay with an ESP of 20, less than 5% of a complete Al-interlayer was enough to prevent a reduction in hydraulic conductivity. Packets in the day systems tested explain the high efficiency of the Fe and Al polycations.