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Different Water Contents (different + water_content)

Distribution by Scientific Domains

Life Sciences	37%
Engineering	37%
Chemistry	25%

Selected Abstracts

Water Dynamics in Ionomer Membranes by Field-Cycling NMR Relaxometry,

FUEL CELLS, Issue 1 2006
J.-C. Perrin
Abstract The water dynamics of two types of ionomer membranes, the Nafion® and sulfonated polyimides, have been investigated by field-cycling nuclear magnetic relaxation. This technique, applied to samples prepared at different water content, allows to characterize the proton motion at the time scale of the microsecond. The polyimides appear to behave as standard porous materials, whereas in the Nafion®, we have observed two different dynamical regimes related to a complex swelling process. [source]

Homologues of nitrite reductases in ammonia-oxidizing archaea: diversity and genomic context

ENVIRONMENTAL MICROBIOLOGY, Issue 4 2010
Rita Bartossek
Summary Ammonia-oxidizing archaea are frequent and ubiquitous inhabitants of terrestrial and marine environments. As they have only recently been detected, most aspects of their metabolism are yet unknown. Here we report on the occurrence of genes encoding potential homologues of copper-dependent nitrite reductases (NirK) in ammonia-oxidizing archaea of soils and other environments using metagenomic approaches and PCR amplification. Two pairs of highly overlapping 40 kb genome fragments, each containing nirK genes of archaea, were isolated from a metagenomic soil library. Between 68% and 85% of the open reading frames on these genome fragments had homologues in the genomes of the marine archaeal ammonia oxidizers Nitrosopumilus maritimus and Cenarchaeum symbiosum. Extensions of NirK homologues with C-terminal fused amicyanin domains were deduced from two of the four fosmids indicating structural variation of these multicopper proteins in archaea. Phylogenetic analyses including all major groups of currently known NirK homologues revealed that the deduced protein sequences of marine and soil archaea were separated into two highly divergent lineages that did not contain bacterial homologues. In contrast, another separated lineage contained potential multicopper oxidases of both domains, archaea and bacteria. More nirK gene variants directly amplified by PCR from several environments indicated further diversity of the gene and a widespread occurrence in archaea. Transcription of the potential archaeal nirK in soil was demonstrated at different water contents, but no significant increase in transcript copy number was observed with increased denitrifying activity. [source]

Conformational changes of ,-lactoglobulin in sodium bis(2-ethylhexyl) sulfosuccinate reverse micelles

FEBS JOURNAL, Issue 4 2004
A fluorescence, CD study
The effect of ,-lactoglobulin encapsulation in sodium bis(2-ethylhexyl) sulfosuccinate reverse micelles on the environment of protein and on Trp was analysed at different water contents (,0). CD data underlined the distortion of the ,-sheet and a less constrained tertiary structure as the ,0 increased, in agreement with a concomitant red shift and a decrease in the signal intensity obtained in steady-state fluorescence measurements. Fluorescence lifetimes, evaluated by biexponential analysis, were ,1 = 1.28 ns and ,2 = 3.36 ns in neutral water. In reverse micelles, decay-associated spectra indicated the occurrence of important environmental changes associated with ,0. Bimolecular fluorescence quenching by CCl4 and acrylamide was employed to analyse alterations in the accessibility of the two Trp residues in ,-lactoglobulin, induced by changes in ,0. The average bimolecular quenching constant <> was found not to depend on ,0, confirming the insolubility of this quencher in the aqueous interface, while <> increases with ,0. The drastic decrease with ,0 of kq, associated with the longest lifetime, , comparatively to the increase of , emphasizes the location of ,-lactoglobulin in the aqueous interfacial region especially at ,0,,10. The fact that (,0 = 30) , (water) also confirms the important conformational changes of encapsulated ,-lactoglobulin. [source]

Micromechanical aspects of the shear strength of wet granular soils

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2008
U. El Shamy
Abstract This paper presents a micromechanical model for the analysis of wet granular soils at low saturation (below 30%). The discrete element method is employed to model the solid particles. The capillary water is assumed to be in a pendular state and thus exists in the form of liquid bridges at the particle-to-particle contacts. The resulting inter-particle adhesion is accounted for using the toroidal approximation of the bridge. Hydraulic hysteresis is accounted for based on the possible mechanism of the formation and breakage of the liquid bridges during wetting and drying phases. Shear test computational simulations were conducted at different water contents under relatively low net normal stresses. The results of these simulations suggest that capillary-induced attractive forces and hydraulic hysteresis play an important role in affecting the shear strength of the soil. These attractive forces produce a tensile stress that contributes to the apparent cohesion of the soil and increases its stiffness. During a drying phase, capillary-induced tensile stresses, and hence shear strength, tend to be larger than those during a wetting phase. The proposed model appears to capture the macroscopic response of wet granular materials and revealed a number of salient micromechanical mechanisms and response patterns consistent with theoretical considerations. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Stabilization of soft clay in irrigation projects,

IRRIGATION AND DRAINAGE, Issue 2 2005
M. M. Mubeen
stabilisation de chaux; utilisation d'argile molle; déchet de pierre pulvérisée; ouvrage d'irrigation Abstract Clay,lime improvement is an effective means to improve soft clay soil. Lime stabilization especially improves the strength and the workability of the clay soil. In addition, lime improvement provides more resistance to the soil structure and to the effect of weather on the soil structure. This study has investigated lime stabilization of soft clay and the possibility of utilizing waste rock powder produced in crusher plants as a supplemental material for lime stabilization in order to increase the strength of the soil structure. The purpose of the study was to apply the results especially in irrigation projects in order to avoid the problems of soft clay on irrigation structures in Sri Lanka. However, the results and conclusions can be considered for other regions, where the same type of soft clay problems exists. The Dutch Oostvaardersplassen (OVP) soft clay, which has a high plasticity, low shear strength and high natural water content, was chosen for the investigations. The results of unconfined compressive strength for different water contents of clay and also for different lime and waste rock powder contents show an excellent increase in strength and workability. The waste rock powder proved to increase the effect of lime stabilization. The strength improvement caused by waste rock powder is more significant for those soils which have a low clay content. Since in irrigation projects a wide range of clay soils exist, this investigation may be useful to utilize waste rock powder in order to improve the quality and the durability of the foundation of irrigation structures in the long run. Therefore the application of lime and rock material improvement on soft clay in irrigation projects may be a useful approach to stabilize soft soils and improve medium-scale shallow foundation irrigation structures and road and canal embankments, including repairing canal leaks. It has also been found that by applying this method in irrigation projects in Sri Lanka, the stabilization cost for structures on soft clay can be significantly reduced compared to other methods. Copyright © 2005 John Wiley & Sons, Ltd. L'amélioration de l'argile avec de la chaux est une moyenne effective pour améliorer la terre de l'argile molle. Spécialement la stabilisation de chaux améliore la force et la maniabilité de la terre argileuse. De plus l'amélioration de chaux fournit plus de résistance à la structure de la terre avec l'effet du temps sur la structure de la terre pendant les conditions atmosphériques différentes. Dans cette étude on a examiné la stabilisation de chaux dans l'argile molle et la possibilité de utiliser des déchets de pierre pulvérisée, obtenus par pulvériser des usines, comme une matérielle supplémentaire pour la stabilisation de chaux afin que la force de la structure de la terre s'améliore. L'objective de cette étude était d'appliquer les résultats spécialement dans des projets d'irrigation pour éviter des problèmes de l'argile molle dans des structures d'irrigation en Sri Lanka. Les résultats et les conclusions peuvent être considérés pour d'autres régions, ayant le même problème de l'argile molle. Les Oostvaarderplassen (OVP) en Hollande ont de l'argile molle ayant une plasticité haute, une résistance au cisaillement basse et un haut pourcentage de l'eau naturelle. C'est pour ça les Oostvaardersplassen ont été choisis pour accomplir la recherche. Les résultats de la force de pression indéfinie pour des teneurs en eau différents dans l'argile, aussi pour les teneurs en chaux différents et des déchets de pierres pulvérisées montrent une augmentation excellente de la force et de la maniabilité. Les déchets de pierre pulvérisée se révèlent d'augmenter l'effet de la stabilisation de chaux. L'amélioration de la force, causée par les déchets de pierre pulvérisée, est plus significative pour ces terres ayant un teneur d'argile bas. Parce que les projets d'irrigation ont beaucoup de la terre d'argile cette recherche peut être utile pour user des déchets de pierre pulvérisée pour améliorer la qualité et la durabilité de la fondation des structures d'irrigation à long terme. C'est pourquoi l'application du matériel de chaux et de pierre sur de l'argile molle dans des projets d'irrigation peut être une approche utile pour stabiliser des terres molles et peut améliorer des structures de fondations d'irrigation dans des eaux pas profondes, dans des remblais de chemins et de canaux, inclus dans des réparations des fuites de canaux. Aussi on a révélé qu'en appliquant ce méthode dans des projets d'irrigation en Sri Lanka les coûts de la stabilisation des structures sur de l'argile molle peuvent être réduits d'une manière importante comparée avec d'autres méthodes. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Phase behaviour of microemulsions with lubricant base oil as the oil phase

LUBRICATION SCIENCE, Issue 7 2009
Ya Lu
Abstract Appropriate surfactants and co-surfactants were chosen to prepare a microemulsion system with lubricant base oil as the oil phase. The phase behaviour of the microemulsion at different temperatures and at different oil/water mass ratios was assessed on the basis of conductivity measurements. Microemulsions and a bi-continuous microstructure were obtained when the oil/water mass ratio was below 0.33. An analysis of the conductivity behaviour of the microemulsions revealed that different conductive mechanisms are operative at different water contents. Activation energies (,E) were determined. The results showed that ,E increases with increasing water content. The data and the derived relationship provided a basis for preparing metalworking microemulsions. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Chlorophyll a Self-assembly in Polar Solvent,Water Mixtures ,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2000
Radka Vladkova
ABSTRACT The conversion of chlorophyll a (Chl a) monomers into large aggregates in six polar solvents upon addition of water has been studied by means of absorption, fluorescence spectroscopy and fluorescence lifetime measurements for the purpose of elucidating the various environmental factors promoting Chl a self-assembly and determining the type of its organization. Two empirical solvent parameter scales were used for quantitative characterization of the different solvation properties of the solvents and their mixtures with water. The mole fractions of water f1/2 giving rise to the midpoint values of the relative fluorescence quantum yield were determined for each solvent, and then various solvent,water mixture parameters for the f1/2 values were compared. On the basis of their comparison, it is concluded that the hydrogen-bonding ability and the dipole,dipole interactions (function of the dielectric constant) of the solvent,water mixtures are those that promote Chl a self-assembly. The influence of the different nature of the nonaqueous solvents on the Chl aggregation is manifested by both the different water contents required to induce Chl monomer , aggregate transition and the formation of two types of aggregates at the completion of the transition: species absorbing at 740,760 nm (in methanol, ethanol, acetonitrile, acetone) and at 667,670 nm (in pyridine and tetrahydrofuran). It is concluded that the type of Chl organization depends on the coordination ability and the polarizability (function of the index of refraction) of the organic solvent. The ordering of the solvents with respect to the f1/2 values,methanol < ethanol < acetonitrile < acetone < pyridine < tetrahydrofuran,yielded a typical lyotropic (Hofmeister) series. On the basis of this solvent ordering and the disparate effects of the two groups of solvents on the Chl a aggregate organization, it is pointed out that the mechanism of Chl a self-assembly in aqueous media can be considered a manifestation of the Hofmeister effect, as displayed in the lipid-phase behavior (Koynova et al., Eur. J. Biophys. 25, 261,274, 1997). It relates to the solvent ability to modify the bulk structure and to distribute unevenly between the Chl,water interface and bulk liquid. [source]

Human skin permittivity determined by millimeter wave reflection measurements

BIOELECTROMAGNETICS, Issue 5 2007
S.I. Alekseev
Abstract Millimeter wave reflection from the human skin was studied in the frequency range of 37,74 GHz in steps of 1 GHz. The forearm and palm data were used to model the skin with thin and thick stratum corneum (SC), respectively. To fit the reflection data, a homogeneous unilayer and three multilayer skin models were tested. Skin permittivity in the mm-wave frequency range resulted from the permittivity of cutaneous free water which was described by the Debye equation. The permittivity increment found from fitting to the experimental data was used for determination of the complex permittivity and water content of skin layers. Our approach, first tested in pure water and gelatin gels with different water contents, gave good agreement with literature data. The homogeneous skin model fitted the forearm data well. Permittivity of the forearm skin obtained with this model was close to the skin permittivity reported by others. To fit reflection from the palmar skin with a thick SC, a skin model containing at least two layers was required. Multilayer models provided better fitting to both the forearm and palmar skin reflection data. The fitting parameters obtained with different models were consistent with each other. Bioelectromagnetics 28:331,339, 2007. © 2007 Wiley-Liss, Inc. [source]