Values Characteristic (value + characteristic)

Distribution by Scientific Domains

Selected Abstracts

Bubble coalescence and its effect on dynamic foam stability

Yoon Seong Cho
Abstract The size of bubbles generated using a single-hole sparger, a multi-hole sparger and a flotation cell were measured. While the size of bubbles generated from the single-hole sparger does not depend on frother concentration, the bubble size strongly depends on frother concentration when the multi-hole sparges, or flotation cell, are utilized. The bubbles size ceases to depend on frother at the concentrations exceeding the value characteristic for each frother and referred to as the critical coalescence (CCC). All the bubble size vs. frother concentration curves converge on a single curve. Aqueous solutions of the frothers that are characterized by low CCC values from foams quite stable under dynamic conditions. Since bubble coalescence can be inhibited by frother concentrations exceeding the CCC, sparing systems can be studied and compared only at frother concentrations that exceed CCC. On a mesuré la taille des bulles produites par un aérateur à orifice unique, un aérateur à orifices multiples et une cellule de flottation. Alors que la taille des bulles produites avec l'aérateur à orifice unique n'est pas liée à la concentration d'agent moussant, la taille des bulles dépend fortement de la concentration d'agent moussant dans le cas des aérateurs à orifices multiples ou de la cellule de flottation. La taille des bulles cesse d'êde la valeur caractéristique de chaque agent moussant (concentration de coalescence critique ou CCC). Toutes les courbes de taille des bulles par rapport à la concentration d'agent moussant se superposent. Les solutions aqueuses des agents moussants qui sont caractérisés par de faibles valeurs de CCC forment des mousses plutôt stables dans des conditions dynamiques. Considérant que la coalescence es bulles peut être inhibée par des concentrations d'agent moussant excédant la CCC, les systèmes de dispersion peuvent être étudiés et comparés seulemetn à des concentrations d'agent moussant qui excèdent la CCC. [source]

Seismic anisotropy of shales

C.M. Sayers
ABSTRACT Shales are a major component of sedimentary basins, and they play a decisive role in fluid flow and seismic-wave propagation because of their low permeability and anisotropic microstructure. Shale anisotropy needs to be quantified to obtain reliable information on reservoir fluid, lithology and pore pressure from seismic data, and to understand time-to-depth conversion errors and non-hyperbolic moveout. A single anisotropy parameter, Thomsen's , parameter, is sufficient to explain the difference between the small-offset normal-moveout velocity and vertical velocity, and to interpret the small-offset AVO response. The sign of this parameter is poorly understood, with both positive and negative values having been reported in the literature. , is sensitive to the compliance of the contact regions between clay particles and to the degree of disorder in the orientation of clay particles. If the ratio of the normal to shear compliance of the contact regions exceeds a critical value, the presence of these regions acts to increase ,, and a change in the sign of ,, from the negative values characteristic of clay minerals to the positive values commonly reported for shales, may occur. Misalignment of the clay particles can also lead to a positive value of ,. For transverse isotropy, the elastic anisotropy parameters can be written in terms of the coefficients W200 and W400 in an expansion of the clay-particle orientation distribution function in generalized Legendre functions. For a given value of W200, decreasing W400 leads to an increase in ,, while for fixed W400, , increases with increasing W200. Perfect alignment of clay particles with normals along the symmetry axis corresponds to the maximum values of W200 and W400, given by and . A comparison of the predictions of the theory with laboratory measurements shows that most shales lie in a region of the (W200, W400)-plane defined by W400/W200,Wmax400/Wmax200. [source]

Binding of proteins to the minor groove of DNA: What are the structural and energetic determinants for kinking a basepair step?

David Bosch
Abstract The structural and energetic determinants for kinking a basepair step by minor groove,insertion of the protein side chains of PurR, LacI, LEF,1, IHF, Sac7d, and Sso7d, have been calculated by molecular dynamics/potential of mean force simulations. The structural determinants of the kinked structures are: two contiguous furanose rings achieve different conformations, in the region of C3,endo (A,DNA) and C2,endo (B,DNA); the , torsion angle always takes values characteristic of the C2,endo conformation of B,DNA, independently of sugar puckering; and protein side chain insertion increases slide (from negative to positive values), rise, and roll, and decreases twist. The energetic determinants of DNA kinking are: the conformational transition of the sugar,phosphate backbone is not energetically demanding; the relative importance of the interbase parameters in the free energy penalty is slide, followed by twist and rise, and concluding with shift and roll; and the characteristic increase of roll and decrease of twist, upon side chain insertion, tends to stabilize the process of DNA kinking. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 682,691, 2003 [source]

Long distance migration and marine habitation in the tropical Asian catfish, Pangasius krempfi

Z. Hogan
A synthesis of catch data from southern Laos and life-history information indicate that adult Pangasius krempfi, an important Asian catfish, migrates up the Mekong River from the South China Sea in Vietnam past Cambodia, arriving in southern Laos each year in May. Strontium concentrations in the otoliths of river-caught P. krempfi are, on average, three to four times higher than the levels of strontium in the otoliths of related freshwater species, indicating marine and estuary habitation for fish caught in southern Laos. Pangasius krempfi muscle tissue samples from the same fish also exhibit stable isotope (,15N and ,13C) values characteristic of marine environments. The results of this investigation support the conclusion that P. krempfi is anadromous, spending a part of its life at sea and in the brackish water of the Mekong Delta before returning to spawn in fresh water. The fish travels at least 720 km to the Khone Falls in southern Laos, and possibly further. Spawning probably occurs in fresh water from June to August at which time young fish move down the Mekong River to the Mekong Delta. The data answer a previously unresolved question (the long-distance migratory behaviour of P. krempfi) and have important implications for the management and conservation of Mekong River fishes. [source]

Technology, genres, and value change: The case of little magazines

Stephen Paling
Producers in creative genres are frequently motivated by goals that put those producers in opposition to popular culture and marketplace pressures. Questions about whether those goals reflect values that belong specifically to print culture, or whether those values will continue to motivate producers in creative genres after the introduction of online technology, have not been answered empirically. Previous studies of genre change have been among those that have focused on the ability of human actors to use information technology to alter those genres as social structures. However, these studies have focused on generic artifacts rather than on the creative values that motivated the creation of those artifacts. Editors of small literary magazines (generally referred to as little magazines) make ideal subjects for this study. Creative values play an important role in their decisions, and they frequently publish poetry, fiction, and other work that stand in opposition to popular culture and literature. This study proposed and evaluated a conceptual framework for anticipating whether editors of little magazines will use online technologies to reinforce or alter the values characteristic of their genre. The study found that the values posited in the conceptual framework fit the goals expressed by little magazine editors. Not all editors held those values equally, however. These findings suggest that producers in creative genres can use online technology in ways that actually reflect an intensification of those values. The concept of intensifying use of technology (IUT) was posited to explain the differences. [source]

Hot carrier energy losses in conducting layers of AlGaN/GaN heterostructures grown on SiC and Al2O3 substrates

B. A. Danilchenko
Abstract The energy relaxation rate for hot electrons in AlGaN/GaN heterostructures was measured over the temperature range 4.2,300 K. Samples grown on sapphire and 4H-SiC substrates were studied. The most important result is that the hot carrier energy dissipation differs for samples grown on sapphire and SiC substrates. In the case of sapphire substrate, the dissipation can be described by the emission of optical phonons with an energy of 90 meV and relaxation time of 25 fs. In the case of SiC substrate, both activation energy and relaxation time exceed the values characteristic of the electron-LO-phonon dissipation process. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Black and white , does melanin change the bulk carbon and nitrogen isotope values of feathers?

Andreas Michalik
Bird feathers are employed in a wide range of carbon and nitrogen isotope studies relating to diet and migration. Feathers are chemically inert with respect to carbon and nitrogen, after synthesis. It has always been assumed that feathers show isotope values characteristic of keratin, a fibrous structural protein from which they are formed. Little attention has been paid to other components of feathers such as melanin or carotenoids. Melanin is synthesized from tyrosine, which is depleted in both 13C and 15N. We compared isotope values of coeval black and white feathers in four different species. Black feather parts were in all cases significantly depleted in 13C relative to white feather parts but in most species no clear trend was discernable for 15N. We suggest that additional evaluation may be required to characterize the carbon and nitrogen isotope contribution of feather pigments like carotenoids. Care should be taken in future stable isotope studies when comparing differently coloured feathers. Copyright © 2010 John Wiley & Sons, Ltd. [source]