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Various Ranges (various + range)

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Earth and Environmental Science	50%

Selected Abstracts

Equations of state for basin geofluids: algorithm review and intercomparison for brines

GEOFLUIDS (ELECTRONIC), Issue 4 2002
J. 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]

Adenosine in the central nervous system: release mechanisms and extracellular concentrations

JOURNAL OF NEUROCHEMISTRY, Issue 3 2001
Serena Latini
Adenosine has several functions within the CNS that involve an inhibitory tone of neurotransmission and neuroprotective actions in pathological conditions. The understanding of adenosine production and release in the brain is therefore of fundamental importance and has been extensively studied. Conflicting results are often obtained regarding the cellular source of adenosine, the stimulus that induces release and the mechanism for release, in relation to different experimental approaches used to study adenosine production and release. A neuronal origin of adenosine has been demonstrated through electrophysiological approaches showing that neurones can release significant quantities of adenosine, sufficient to activate adenosine receptors and to modulate synaptic functions. Specific actions of adenosine are mediated by different receptor subtypes (A1, A2A, A2B and A3), which are activated by various ranges of adenosine concentrations. Another important issue is the measurement of adenosine concentrations in the extracellular fluid under different conditions in order to know the degree of receptor stimulation and understand adenosine central actions. For this purpose, several experimental approaches have been used both in vivo and in vitro, which provide an estimation of basal adenosine levels in the range of 50,200 nm. The purpose of this review is to describe pathways of adenosine production and metabolism, and to summarize characteristics of adenosine release in the brain in response to different stimuli. Finally, studies performed to evaluate adenosine concentrations under physiological and hypoxic/ischemic conditions will be described to evaluate the degree of adenosine receptor activation. [source]

Synthesis of poly(fluorinated styrene)- block -poly(ethylene oxide) amphiphilic copolymers via atom transfer radical polymerization: potential application as paper coating materials

POLYMER INTERNATIONAL, Issue 8 2009
Khalid A Ibrahim
Abstract BACKGROUND: The surface of a substrate which comprises a fibrous material is brought into contact with a type of amphiphilic block copolymer which comprises hydrophilic/hydrophobic polymeric blocks. These amphiphilic copolymers have been synthesized by atom transfer radical polymerization (ATRP) technique. The atom transfer radical polymerization of poly(2,3,4,5,6-pentafluorostyrene)- block -poly(ethylene oxide) (PFS- b -PEO) copolymers (di- and triblock structures) with various ranges of PEO molecular weights was initiated by a PEO chloro-telechelic macroinitiator. The polymerization, carried out in bulk and catalysed by copper(I) chloride in the presence of 2,2,-bipyridine ligand, led to A,B,A amphiphilic triblock and A,B amphiphilic diblock structures. RESULTS: With most of the macroinitiators, the living nature of the polymerizations led to block copolymers with narrow molecular weight distributions (1.09 < Mw/Mn < 1.33) and well-controlled molecular structures. These block copolymers turned out to be water-soluble through adjustment of the PEO block content (>90 wt%). Of all the block copolymers synthesized, PFS- b -PEO(10k)- b -PFS containing 10 wt% PFS was found to retard water absorption considerably. CONCLUSION: The printability of paper treated with the copolymers was evaluated with contact angle measurements and felt pen tests. The adsorption of such copolymers at the solid/liquid interface is relevant to the wetting and spreading of liquids on hydrophobic/hydrophilic surfaces. Copyright © 2009 Society of Chemical Industry [source]

Assessing vertical resolution requirements for operational weather radar data quality

ATMOSPHERIC SCIENCE LETTERS, Issue 1 2006
Marion P. Mittermaier
Abstract High-resolution, 0.28° beamwidth range-height-indicator (RHI) data are used to simulate the reflectivities measured at various ranges by an operational radar with a 1° beamwidth. It is found that the sampling is optimal when the elevation increments equal the beamwidth. Larger increments lead to an unacceptable loss of information. Copyright © 2006 Royal Meteorological Society [source]