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  • 1
    Electronic Resource
    Electronic Resource
    Distribution of Nonadrenergic [3H]Rilmenidine Binding in Rat Brain and Kidney (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 763 (1995), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1995.tb32407.x
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  • 2
    Electronic Resource
    Electronic Resource
    Effective properties for flow calculations (1995)
    Springer
    Transport in porous media 20 (1995), S. 169-196 
    Details
    ISSN: 1573-1634
    Keywords: effective flow properties ; reservoir geology ; permeability ; transmissibility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract In this paper we discuss the background to the problems of finding effective flow properties when moving from a detailed representation of reservoir geology to a coarse gridded model required for reservoir performance simulation. In so doing we synthesize the pictures of permeability and transmissibility and show how they may be used to capture the effects of the boundary conditions on the upscaling. These same concepts are applied to the renormalization method of calculating permeability, to show its promise as an accurate, yet fast method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00616929
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  • 3
    Electronic Resource
    Electronic Resource
    Upscaling permeability: Error analysis for renormalization (1996)
    Springer
    Transport in porous media 23 (1996), S. 337-354 
    Details
    ISSN: 1573-1634
    Keywords: numerical simulation ; upscaling ; renormalisation ; error analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract In this paper we briefly discuss the background to the problems of finding effective flow properties when moving from a detailed representation of reservoir geology to a coarse gridded model required for reservoir performance simulation. The basic requirements for the upscaled properties are also discussed. We then consider one technique, renormalization, that in recent years has shown promise as an accurate, yet fast, method. The mathematical background of the renormalization approach is examined. A rigorous formalism is developed that allows an explicit calculation of the error terms to be made. In a very simple case use of the correction terms is shown to produce a dramatic improvement in accuracy of the method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00167102
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  • 4
    Electronic Resource
    Electronic Resource
    Generation of correlated properties in heterogeneous porous media (1988)
    Springer
    Mathematical geology 20 (1988), S. 863-877 
    Details
    ISSN: 1573-8868
    Keywords: Spatial variability ; random field ; correlation ; stochastic models ; Monte Carlo simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract The spatial distribution of rock properties in porous media, such as permeability and porosity, often is strongly variable. Therefore, these properties usefully may be considered as a random field. However, this variability is correlated frequently on length scales comparable to geological lengths (for example, scales of sand bodies or facies). To solve various engineering problems (for example, in the oil recovery process) numerical models of a porous medium often are used. A need exists then to understand correlated random fields and to generate them over discretized numerical grids. The paper describes the general mathematical methods required to do this, with one particular method (the nearest neighbor model) described in detail. How parameters of the mathematical model may be related to rock property statistics for the nearest neighbor model is shown. The method is described in detail in one, two, and three dimensions. Examples are given of how model parameters may be determined from real data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00890196
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  • 5
    Electronic Resource
    Electronic Resource
    Renormalization calculations of immiscible flow (1993)
    Springer
    Transport in porous media 12 (1993), S. 237-260 
    Details
    ISSN: 1573-1634
    Keywords: Effective properties ; relative permeability ; pseudoization ; rescaling ; heterogeneity ; simulation ; reservoir characterization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Oil reservoir properties can vary over a wide range of length scales. Reservoir simulation of the fluid flow uses numerical grid blocks have typical lengths of hundreds of metres. We need to specify meaningful values to put into reservoir engineering calculations given the large number of heterogeneities that they have to encompass. This process of rescaling data results in the calculation of ‘effective’ or ‘pseudo’ rock properties. That is a property for use on the large scale incorporating the many heterogeneities measured on smaller scales. For single phase flow, a variety of techniques have been tried in the past. These range from very simple statistical estimates to detailed numerical simulation. Unfortunately, the simple estimates tend to be inaccurate in real applications and the numerical simulation can be computationally expensive if not impossible for very fine grid representations of the reservoir. Likewise, pseudorelative permeabilities are time consuming to generate and often inaccurate. Real-space renormalization is an alternative technique which has been found to be computationally efficient and accurate when applied to single-phase flow. This approach solves the problem regionally rather than trying to solve the whole problem in one simulation. The effective properties of small regions are first calculated and then placed on a coarse grid. The grid is further coarsened and the process repeated until a single effective property has been calculated. This has enabled calculation of effective permeability of extremely large grids to be performed, up to 540 million grid blocks in one application. This paper extends the renormalization technique to two-phase fluid flow and shows that the method is at least 100 times faster than conventional pseudoization techniques. We compare the results with high resolution numerical simulation and conventional pseudoization methods for three different permeability models. We show that renormalization is as accurate as the conventional methods when used to predict oil recovery from heterogeneous systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00624460
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  • 6
    Electronic Resource
    Electronic Resource
    The use of renormalization for calculating effective permeability (1989)
    Springer
    Transport in porous media 4 (1989), S. 37-58 
    Details
    ISSN: 1573-1634
    Keywords: Heterogeneity ; effective permeability ; scaling ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract There is a need in the numerical simulation of reservoir performance to use average permeability values for the grid blocks. The permeability distributions to be averaged over are based on samples taken from cores and from logs using correlations between permeabilities and porosities and from other sources. It is necessary to use a suitable ‘effective’ value determined from this sample. The effective value is a single value for an equivalent homogeneous block. Conventionally, this effective value has been determined from a simple estimate such as the geometric mean or a detailed numerical solution of the single phase flow equation. If the permeability fluctuations are small then perturbation theory or effective medium theory (EMT) give reliable estimates of the effective permeability. However, for systems with a more severe permeability variation or for those with a finite fraction of nonreservoir rock all the simple estimates are invalid as well as EMT and perturbation theory. This paper describes a real-space renormalization technique which leads to better estimates than the simpler methods and is able to resolve details on a much finer scale than conventional numerical solution. Conventional simulation here refers to finite difference (or element) techniques for solving the single phase pressure equation. This requires the pressure and permeability at every grid point to be stored. Hence, these methods are limited in their resolution by the amount of data that can be stored in core. Although virtual memory techniques may be used they increase computer time. The renormalization method involves averaging over small regions of the reservoir first to form a new ‘averaged permeability’ distribution with a lower variance than the original. This pre-averaging may be repeated until a stable estimate is found. Examples are given to show that this is in excellent agreement with computationally more expensive numerical solution but significantly different from simple estimates such as the geometric mean.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00134741
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  • 7
    Electronic Resource
    Electronic Resource
    Coagulation of blood at the tip of optical fibres used for light delivery in photodynamic therapy (1989)
    Springer
    Lasers in medical science 4 (1989), S. 125-129 
    Details
    ISSN: 1435-604X
    Keywords: Photodynamic therapy ; Diffusing fibre tips ; Interstitial light delivery ; Light dosimetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Optimal delivery of light to the tumour is of considerable importance in photodynamic therapy. The most effective way of delivering laser light to the tumour tissue is through an implanted optical fibre. In order to investigate the possible effects taking place at the tips of fibres implanted in tissue, fibres were used to deliver light to human blood and the transmission of light by the blood was measured at different power levels. The maximum power level which could be delivered without charring or coagulation at the fibre tip was measured for five different fibres. Three plane cut fibres and two with 1.5 cm long diffusing tips were studied. Charring and coagulation, which resulted in practically no light being delivered more than 0.5 mm from the fibre tip, were observed at relatively low-output powers (70-130 mW) for all the plane-cut fibres. This is less than the level required to deliver a clinically useful dose in a reasonable time. In contrast, neither charring nor coagulation was observed at the diffusing tips for output powers up to 1.1 W and consequently these should be the fibres of choice for interstitial photodynamic therapy. Observed changes in light transmission through the blood with increasing output power indicate that, for accurate light dosimetry, a means of monitoring delivered light in vivo during photodynamic therapy is essential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02032609
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  • 8
    Electronic Resource
    Electronic Resource
    A method for the construction of disposable cylindrical diffusing fibre optic tips for use in photodynamic therapy (1989)
    Springer
    Lasers in medical science 4 (1989), S. 229-235 
    Details
    ISSN: 1435-604X
    Keywords: Photodynamic therapy ; Cylindrical diffuser ; Interstitial treatment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract A simple method for the manufacture of disposable, cylindrical, diffusing fibre tips is described. The method is suitable for plastic clad silica fibres with core diameters in the range 200–600μm. Light diffusing tips up to 40 mm in length have been constructed. The method is highly reproducible, construction is typically less than five minutes and the financial cost is negligible. The diffusers are highly efficient, delivering an amount of light at least equal to that transmitted by a plane cut fibre of the same core diameter. The uniformity of light emission along the diffuser can be modified to meet the requirements of any given treatment. The diffusers have been successfully used in interstitial photodynamic therapy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02032452
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  • 9
    Electronic Resource
    Electronic Resource
    Light delivery to tumour tissue through implanted optical fibres during photodynamic therapy (1990)
    Springer
    Lasers in medical science 5 (1990), S. 345-350 
    Details
    ISSN: 1435-604X
    Keywords: Photodynamic therapy ; Light transmission in tissue
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract The maximum rate at which the light dose may be delivered during interstitial photodynamic therapy (PDT) has been measured for several types of delivery fibre. Measurements of light irradiance at the skin surface overlying subcutaneous experimental tumours were made during interstitial irradiation by 200Μm core diameter fibres whose output ends were either plane-cut or 5 mm long cylindrical diffusers. For plane-cut fibres, a rapid fall in light transmission, due to blood coagulation at the fibre tip, was observed at output powers greater than 229 mW and 104 mW in tumours with and without photosensitizer, respectively. Such a rapid fall was not observed with cylindrical diffusing fibres at output powers up to 1 W. In the clinical use of PDT the fibre output power is held constant at a level below which thermal effects may occur. In a second study, therefore, the irradiance at the skin surface was monitored for this treatment regime. A decrease in light transmission during treatment was observed. Plane-cut fibres showed a greater decrease than cylindrical diffusing fibres and for a given fibre type, non-photosensitized tumours showed a greater decrease than photosensitized tumours. For cylindrical diffusing fibres at output powers of 150 mW or less there was a 9% decrease in irradiance measured at the skin surface during the first 1000 s of treatment. The decrease was larger (30–40%) for fibre output powers in the range 200–300 mW.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02032590
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  • 10
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    The optical properties of aqueous suspensions of Intralipid, a fat emulsion (1989)
    Institute of Physics
    Details
    Publication Date: 1989-12-01
    Print ISSN: 0031-9155
    Electronic ISSN: 1361-6560
    Topics: Biology , Medicine , Physics
    Published by Institute of Physics
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