Home About us Contact
|
Home About us Contact | ||
|
|
||
Water Density (water + density)
Selected AbstractsKinetic model for noncatalytic supercritical water gasification of cellulose and ligninAICHE JOURNAL, Issue 9 2010Fernando L. P. Resende Abstract This article reports the first kinetics model for Supercritical Water Gasification (SCWG) that describes the formation and interconversion of individual gaseous species. The model comprises 11 reactions, and it uses a lumping scheme to handle the large number of intermediate compounds. We determined numerical values for the rate constants in the model by fitting it to experimental data previously reported for SCWG of cellulose and lignin. We validated the model by showing that it accurately predicts gas yields at biomass loadings and water densities not used in the parameter estimation. Sensitivity analysis and reaction rate analysis indicate that steam-reforming and water,gas shift are the main sources of H2 in SCWG, and intermediate species are the main sources of CO, CO2, and CH4. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Complete dissolution and hydrolysis of wood in hot waterAICHE JOURNAL, Issue 10 2008Zhen Fang Abstract When willow and water were heated rapidly (7,16°C/s) to high temperatures and high pressures, most of willow (90 vol %) dissolved in water at 341°C in 2.5 s without complete dissolution. Adding 0.8 wt % Na2CO3, complete dissolution of willow (concentration up to 35 vol %) was observed at 329,367°C and water densities of 322,787 kg/m3 (14,106 MPa) in 1.5 s. By cooling the solublized willow immediately, micron particles were obtained via precipitation. If heated further to 400°C, willow was completely hydrolyzed to sugars/sugar oligomers in 14.6 s at homogeneous conditions. A flow reactor was proposed to completely solubilize willow for the production of micron particles, sugars, bio-fuels and chemicals continuously. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] Effect of light and predator abundance on the habitat choice of plant-attached zooplanktonFRESHWATER BIOLOGY, Issue 3 2007LEENA NURMINEN Summary 1. The diurnal variations in the habitat choice of the periodically plant-attached cladoceran Sida crystallina together with light environment and predator abundance were studied. 2. The density of S. crystallina attached to floating leaves of Nuphar lutea increased between 18:00 and 20:00 hours, when light intensity underneath the leaves was temporarily increased, and decreased again when light intensity declined. A proportion of S. crystallina remained in the swimming mode underneath the leaves even during daylight, indicating that the water column sheltered by the leaves is safer than the open water. 3. In the water adjacent to the leaves, the density of S. crystallina increased steeply in the dark. The increase was not accompanied by a decrease in S. crystallina attached to plant leaves, indicating that the nocturnal increment in the open water density of S. crystallina was due to migration from daytime refuges other than floating leaves. 4. Sida crystallina was most intensively consumed by perch (Perca fluviatilis). Predation threat by fish had weaker effects on the density of S. crystallina attached to plant leaves than on cladocerans in the adjacent water. Cladocerans underneath floating plant leaves, whether attached or not, are probably less vulnerable to fish predation than those outside the leaf cover. 5. The results suggested that light intensity is the proximate factor regulating the attachment of zooplankton to the lower surfaces of floating macrophyte leaves. Light intensity has a positive effect on the density of S. crystallina attached to the floating leaves and a negative effect on density in the water. Predation threat by fish has a strong effect on the migration of zooplankters into the open water habitat. [source] Equations of state for basin geofluids: algorithm review and intercomparison for brinesGEOFLUIDS (ELECTRONIC), Issue 4 2002J. J. Adams ABSTRACT Physical properties of formation waters in sedimentary basins can vary by more than 25% for density and by one order of magnitude for viscosity. Density differences may enhance or retard flow driven by other mechanisms and can initiate buoyancy-driven flow. For a given driving force, the flow rate and injectivity depend on viscosity and permeability. Thus, variations in the density and viscosity of formation waters may have or had a significant effect on the flow pattern in a sedimentary basin, with consequences for various basin processes. Therefore, it is critical to correctly estimate water properties at formation conditions for proper representation and interpretation of present flow systems, and for numerical simulations of basin evolution, hydrocarbon migration, ore genesis, and fate of injected fluids in sedimentary basins. Algorithms published over the years to calculate water density and viscosity as a function of temperature, pressure and salinity are based on empirical fitting of laboratory-measured properties of predominantly NaCl solutions, but also field brines. A review and comparison of various algorithms are presented here, both in terms of applicability range and estimates of density and viscosity. The paucity of measured formation-water properties at in situ conditions hinders a definitive conclusion regarding the validity of any of these algorithms. However, the comparison indicates the versatility of the various algorithms in various ranges of conditions found in sedimentary basins. The applicability of these algorithms to the density of formation waters in the Alberta Basin is also examined using a high-quality database of 4854 water analyses. Consideration is also given to the percentage of cations that are heavier than Na in the waters. [source] Structural and dynamic properties of water around acetylcholinesterasePROTEIN SCIENCE, Issue 9 2002Richard H. Henchman AChE, acetylcholinsterase; ARC/TAP, averaged residue coordinate/time-averaged position Abstract Structural and dynamic properties of water molecules around acetylcholinesterase are examined from a 10-nsec molecular dynamics simulation to help understand how the protein alters water properties. Water structure is broken down into hydration sites constructed from the water density <3.6 Å from the protein surface. These sites are characterized according to occupancy, number of water neighbors, hydrogen bonds, dipole moment, and residence time. The site description provides a convenient means to describe the extent and localization of these properties. Determining the network of paths that waters follow from site to site and measuring the rate of flow of waters from the sites to the bulk make it possible to quantitatively study the time scales and paths that water molecules follow as they move around the protein. [source] A review of the biophysical properties of salmonid faeces: implications for aquaculture waste dispersal models and integrated multi-trophic aquacultureAQUACULTURE RESEARCH, Issue 3 2009G K Reid Abstract Knowledge of the quantitative and qualitative properties of salmonid faeces is necessary for aquaculture waste dispersal models, and the design of integrated multi-trophic aquaculture (IMTA) systems. The amount and proximate composition of salmonid faeces can be estimated using a mass-balance, nutritional approach. Indigestible components of salmonid diets have the potential to affect faecal ,cohesiveness' or ,stability'. Nutrient content and density of faeces can vary depending on diet and submersion time. Faecal density has a greater influence on settling velocity than faecal size. Published settling velocity data on salmonid faeces are highly variable due to differences in fish size, rearing systems, collection time, water density, methodology, the mass fraction tested and diet. Most faecal settling data used in published salmonid waste dispersal models are rudimentary and recent information suggests that such models are highly sensitive to this input. The design of open-water IMTA systems and estimation of nutrient capture and recovery from co-cultured filter feeders is difficult due to limited information on particle size, digestibility, settleable and non-settleable mass fractions of salmonid faeces at cage environments. Implications of faecal properties on the accountability for the effects of aquaculture nutrient loading are discussed. [source] Structure and hydration of the amylopectin trisaccharide building blocks,Synthesis, NMR, and molecular dynamicsBIOPOLYMERS, Issue 12 2008Peter I. Hansen Abstract To gain insight into the molecular details and hydration of amylopectin, the five constituting trisaccharides have been chemically synthesized as their methyl ,-glycosides. All five trisaccharides were subjected to 950 MHz NMR spectroscopy for complete assignment and nanosecond molecular dynamics trajectories were calculated to study the structure and dynamics of the trisaccharides in aqueous solution. Systematic analysis of the simulation data revealed several examples of bridging water molecules playing an important role in the stabilization of specific amylopectin conformations, which was also supported by the experimental NMR data such as interresidue NOE's and heteronuclear scalar couplings between nuclei from neighboring residues. Although ,-maltotriose, ,-iso-maltotriose, ,-panose and ,-isopanose are relatively well characterized structures, the study also includes one less characterized trisaccharide with the structure ,Glcp(1,4),Glcp(1,6),Glcp. This trisaccharide, tentatively labelled ,-forkose, is located at the branch point of amylopectin, forking the amylopectin into two strands that align into double-helical segments. The results show that the conformation of ,-forkose takes a natural bend form which fits well into the structure of the double-helical segment of amylopectin. As the only trisaccharide in this study the structure of ,-forkose is not significantly influenced by the hydration. In contrast, ,-isopanose takes a restricted, but rather extended form due to an exceptionally strong localized water density. The two homo-linkage oligomers, ,-maltotriose and ,-iso-maltotriose, showed to be the most extended and the most flexible trimers, respectively, providing regular structure for crystalline domains and maximum linker flexibility for amorphous domains. © 2008 Wiley Periodicals, Inc. Biopolymers 89: 1179,1193, 2008. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] | |||||||||||||