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  • 11
    Electronic Resource
    Electronic Resource
    Reversible formation of bromonium ions. Preferential reaction of Br- on the Br+ of the bromonium ion produced from the solvolysis of trans-2-bromocyclohexyl triflate in methanol or acetic acid containing added bromide (1993)
    s.l. : American Chemical Society
    The @journal of organic chemistry 58 (1993), S. 2122-2127 
    Details
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jo00060a031
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    Paper (German National Licenses)
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  • 12
    Electronic Resource
    Electronic Resource
    Analysis of Ground-Water Remedial Alternatives at a Superfund Site (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 29 (1991), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: This paper presents a simple yet effective approach and methodology for the problem of evaluating ground-water remedial alternatives at a waste disposal site, and discusses the application of this approach in a case study. The attainment areas, which represent the areas (outside the contaminant source itself) in which remediation is required, are first identified. Simulation of ground-water flow in three dimensions, augmented by fluid particle tracking, is utilized to evaluate the travel times of ground water through the attainment areas. The mixed linear reservoir or “batch flush” model is then used to estimate the number of pore volumes which must be flushed through each attainment area in order to achieve remediation. The travel times are used in conjunction with this pore volume figure to estimate the time required for cleanup under each alternative. By comparing the cleanup time, the costs, and other features of each alternative, a cost-effective remedy for the study site can be determined. While the development of remedial alternatives and the choice of the most cost-effective remedy are highly site-specific, the approach and methodology outlined in this paper have general applicability. The results presented herein also provide insight into the difficulties and special considerations associated with modeling and analyzing remedial alternatives.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1991.tb00570.x
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  • 13
    Electronic Resource
    Electronic Resource
    MODFLOW/MT3DMS-Based Reactive Multicomponent Transport Modeling (2003)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 41 (2003), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: This paper presents a three-dimensional, MODFLOW/MT3DMS-based reactive multicomponent transport model for saturated porous media. Based on a split-operator technique, the model, referred to as PHT3D, couples the transport simulator MT3DMS and the geochemical modeling code PHREEQC-2. Through the flexible, generic nature of PHREEQC-2, PHT3D can handle a broad range of equilibrium and kinetically controlled reactive processes, including aqueous complexation, mineral precipitation/dissolution, and ion exchange. The diversity of potential applications is demonstrated through simulation of five existing literature benchmarks and a new three-dimensional sample problem. The model might be applied to simulate the geochemical evolution of pristine and contaminated aquifers as well as their cleanup. The latter problem class includes the natural and enhanced attenuation/remediation schemes of a wide range of organic and inorganic contaminants. Processes/reactions not included in the standard PHREEQC-2 database but typical for this type of application (e.g., NAPL dissolution, microbial growth/decay) can be defined and included via the extensible PHREEQC-2 database file.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2003.tb02588.x
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  • 14
    Electronic Resource
    Electronic Resource
    Analysis of Particle Tracking Errors Associated with Spatial Discretization (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 32 (1994), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: This paper addresses two particular problems which arise in particle tracking calculations because of the spatial discretization used in the block-centered finite-difference flow model. These two problems are: (1) the presence of a “weak” sink or source (i.e., a sink or source that does not result in complete inward or outward gradients on all interfaces of the cell containing the sink or source); and (2) the use of a model grid with varying vertical cell dimensions within an individual layer. While these problems can be mitigated by using a sufficiently fine spatial discretization, there are always computational and practical limitations on the number of model nodes. Two procedures are presented in this paper which minimize particle tracking errors associated with weak sinks/sources or vertically distorted grids. The first procedure uses an approximate analytical solution to define the velocity distribution inside a model cell containing a weak sink/source so that the capture of the particles entering the cell can be determined accurately. The second procedure establishes an automatic adjustment of the particle vertical coordinate according to the degree of vertical grid distortion. These procedures are shown to be effective, and improve the accuracy of particle tracking results under nonideal spatial discretizations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1994.tb00923.x
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  • 15
    Electronic Resource
    Electronic Resource
    Extension of the Method of Characteristics for Simulation of Solute Transport in Three Dimensions (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 31 (1993), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The method of characteristics (e.g., Garder et al., 1964; Konikow and Bredehoeft, 1978) has been widely used in the simulation of solute transport in ground-water systems because of its effectiveness for handling advection-dominated problems. However, the method requires a large amount of computer memory and execution time when it is necessary to track a large number of moving particles, especially in three dimensions. The method can also lead to large mass balance discrepancies under certain circumstances. This paper describes a number of changes which may be made in the traditional method of characteristics approach to mitigate these difficulties. These changes include a dynamic particle allocation procedure, which often reduces dramatically the total number of moving particles needed in a simulation; and a consistent velocity interpolation scheme and higher-order particle tracking techniques, which, coupled with effective handling of particle insertion and deletion at sources and sinks, can provide improved mass balance results. The accuracy of a method-of-characteristics model incorporating these changes is evaluated by comparison with analytical solutions for (1) three-dimensional advection and dispersion in a spherical flow field, and (2) concentration change in a well during an injection/pumping cycle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1993.tb01848.x
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  • 16
    Electronic Resource
    Electronic Resource
    REPLY TO the preceding Discussion by Robert D. McCaleb of “Analysis of Ground-Water Remedial Alternatives at a Superfund Site” (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 30 (1992), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1992.tb02014.x
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  • 17
    Electronic Resource
    Electronic Resource
    Optimal Remediation Policy Selection under General Conditions (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 35 (1997), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A new simulation-optimization model has been developed for the optimal design of ground-water remediation systems under a variety of field conditions. The model couples genetic algorithm (G A), a global search technique inspired by biological evolution, with MODFLOW and MT3D, and two commonly used ground-water flow and solute transport codes. The model allows for multiple management periods in which optimal pumping/injection rates vary with time to reflect the changes in the flow and transport conditions during the remediation process. The objective function of the model incorporates multiple cost terms including the drilling cost, the installation cost, and the costs to extract and treat the contaminated ground water. The simulation-optimization model is first applied to a typical two-dimensional pump-and-treat example with one and three management periods to demonstrate the effectiveness and robustness of the new model. The model is then applied to a large-scale three-dimensional field problem to determine the minimum pumping needed to contain an existing contaminant plume. The optimal solution as determined in this study is compared with a previous solution based on trial-and-error selection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1997.tb00144.x
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    Paper (German National Licenses)
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  • 18
    Electronic Resource
    Electronic Resource
    Role of Interceptor Ditches in Limiting the Spread of Contaminants in Ground Water (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 26 (1988), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The ground-water pattern in the vicinity of an interceptor ditch used for agricultural drainage is simulated using flow and stream function models to explore the possibility of using interceptor ditches to control the spread of agricultural chemicals in shallow aquifers. The concept of the dividing streamline is used to quantify the effectiveness of the interceptor ditch for limiting the spread of potential contaminants. The simulation results suggest that the interceptor ditch may create an effective hydraulic barrier to the movement of agricultural contaminants in ground water, but its effectiveness is subject to seasonal changes in hydrological conditions, including the regional water-table gradient, the distribution of recharge and discharge, and the ditch stage. A quantitative relationship between effectiveness of the ditch and these hydrological conditions is established.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1988.tb00424.x
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  • 19
    Electronic Resource
    Electronic Resource
    Regulation of Surface and Intracellular Expression of CTLA-4 on Human Peripheral T Cells (2001)
    Oxford, UK : Blackwell Science Ltd
    Scandinavian journal of immunology 54 (2001), S. 0 
    Details
    ISSN: 1365-3083
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Cytotoxic T-lymphocyte-associated antigen (CTLA-4) is an important downregulator of T-cell activation. In order to analyze the expression and regulation of CTLA-4 on human peripheral T cells, CTLA-4 mRNA and protein expression were determined using analysis by reverse transcription–polymerase chain reaction (RT–PCR) and FACs, respectively. Intracellular CTLA-4 was constitutively expressed in unstimulated CD4+ and CD8+ T cells. Interleukin (IL)-2 induced a dose-dependent increase of both intracellular and surface expression of CTLA-4 (CD152). Most of the CD4+ and CD8+ cells expressing CTLA-4 also expressed CD25. Interferon (IFN)-γ induced the upregulation of CTLA-4 expression via antigen-presenting cells (APC) activation. The CTLA-4delTM mRNA (550 bp) had a shorter half-life than the full length CTLA-4 mRNA and the expression was downregulated upon activation of the cells by treatment with IL-2. Given an inhibitory role of CTLA-4 and CD4+ CD25+ T cells in immune responses, the present findings suggest that IL-2-induced immunosuppression may result from its stimulatory effect of the CTLA-4 expression.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3083.2001.00985.x
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  • 20
    Electronic Resource
    Electronic Resource
    Time frequency distributions of TMJ sounds (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of oral rehabilitation 18 (1991), S. 0 
    Details
    ISSN: 1365-2842
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: For analysis of time-varying signals such as the TMJ sounds, it is often desirable to know how the frequency components change with time, using methods of time-frequency analysis. The aim of this study was to compare two of the most familiar methods for energy density representation with a newly developed technique. The sounds were recorded with a microphone fastened to the subject's forehead, transformed to the time-frequency domain and displayed as 3D- and contour plots using spectrogram, Wigner distribution (WD), and the reduced interference distribution (RID) to display their time-frequency energy distributions. The spectrogram resolved only the low-frequency components. The WD provided higher resolution but also exhibited strong interference between components. The RID gave a detailed representation of the TMJ signals' relative energy distribution in the time and frequency domains, with a great reduction in the interference or cross terms. The RID therefore appears to be most useful in the application of time-frequency distributions in classification of TMJ sounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2842.1991.tb01685.x
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