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  • Articles  (148,507)
  • Springer  (137,627)
  • American Association for the Advancement of Science  (7,833)
  • American Meteorological Society
  • 1995-1999  (148,507)
  • 1990-1994
  • 1999  (72,754)
  • 1995  (75,753)
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  • 1995-1999  (148,507)
  • 1990-1994
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  • 101
    Electronic Resource
    Electronic Resource
    Statistical Evaluation of Population Data for Calculation of Radioactive Material Transport Accident Risks (1999)
    Springer
    Risk analysis 19 (1999), S. 613-619 
    Details
    ISSN: 1539-6924
    Keywords: accident risk ; population distribution ; RADTRAN ; transportation ; radioactive materials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Calculation of accident dose-risk estimates with the RADTRAN code requires input data describing the population likely to be affected by the plume of radioactive material (RAM) released in a hypothetical transportation accident. In the existing model, population densities within 1/2 mile (0.8 km) of the route centerline are tabulated in three ranges (Rural, Suburban, and Urban). These population densities may be of questionable validity since the plume in the RADTRAN analysis is assumed to extend out to 120 km from the hypothetical accident site. We present a GIS-based population model which accounts for the actual distribution of population under a potential plume, and compare accident-risk estimates based on the resulting population densities with those based on the existing model. Results for individual points along a route differ greatly, but the cumulative accident risks for a sample route of a few hundred kilometers are found to be comparable, if not identical. We conclude, therefore, that for estimation of aggregate accident risks over typical routes of several hundred kilometers, the existing, simpler RADTRAN model is sufficiently detailed and accurate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007077402059
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  • 102
    Electronic Resource
    Electronic Resource
    Editorial on the Nugget Papers (1999)
    Springer
    Risk analysis 19 (1999), S. 685-687 
    Details
    ISSN: 1539-6924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007089704785
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  • 103
    Electronic Resource
    Electronic Resource
    Challenges to the Acceptance of Probabilistic Risk Analysis (1999)
    Springer
    Risk analysis 19 (1999), S. 703-710 
    Details
    ISSN: 1539-6924
    Keywords: probabilistic risk analysis ; subjective judgment ; risk-informed regulation ; robust Bayesian analysis ; human performance ; human error ; management and organizational factors ; corporate culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This paper discusses a number of the key challenges to the acceptance and application of probabilistic risk analysis (PRA). Those challenges include: (a) the extensive reliance on subjective judgment in PRA, requiring the development of guidance for the use of PRA in risk-informed regulation, and possibly the development of “robust” or “reference” prior distributions to minimize the reliance on judgment; and (b) the treatment of human performance in PRA, including not only human error per se but also management and organizational factors more broadly. All of these areas are seen as presenting interesting research challenges at the interface between engineering and other disciplines.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007093805693
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  • 104
    Electronic Resource
    Electronic Resource
    Trust, Emotion, Sex, Politics, and Science: Surveying the Risk-Assessment Battlefield (1999)
    Springer
    Risk analysis 19 (1999), S. 689-701 
    Details
    ISSN: 1539-6924
    Keywords: risk ; risk perception ; risk assessment ; risk communication ; risk management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Risk management has become increasingly politicized and contentious. Polarized views, controversy, and conflict have become pervasive. Research has begun to provide a new perspective on this problem by demonstrating the complexity of the concept “risk” and the inadequacies of the traditional view of risk assessment as a purely scientific enterprise. This paper argues that danger is real, but risk is socially constructed. Risk assessment is inherently subjective and represents a blending of science and judgment with important psychological, social, cultural, and political factors. In addition, our social and democratic institutions, remarkable as they are in many respects, breed distrust in the risk arena. Whoever controls the definition of risk controls the rational solution to the problem at hand. If risk is defined one way, then one option will rise to the top as the most cost-effective or the safest or the best. If it is defined another way, perhaps incorporating qualitative characteristics and other contextual factors, one will likely get a different ordering of action solutions. Defining risk is thus an exercise in power. Scientific literacy and public education are important, but they are not central to risk controversies. The public is not irrational. Their judgments about risk are influenced by emotion and affect in a way that is both simple and sophisticated. The same holds true for scientists. Public views are also influenced by worldviews, ideologies, and values; so are scientists' views, particularly when they are working at the limits of their expertise. The limitations of risk science, the importance and difficulty of maintaining trust, and the complex, sociopolitical nature of risk point to the need for a new approach—one that focuses upon introducing more public participation into both risk assessment and risk decision making in order to make the decision process more democratic, improve the relevance and quality of technical analysis, and increase the legitimacy and public acceptance of the resulting decisions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007041821623
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  • 105
    Electronic Resource
    Electronic Resource
    The Complementary Roles of Mitigation and Insurance in Managing Catastrophic Risks (1999)
    Springer
    Risk analysis 19 (1999), S. 727-738 
    Details
    ISSN: 1539-6924
    Keywords: mitigation ; insurance ; catastrophic risk ; building codes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This paper examines the impact that insurance coupled with specific risk mitigation measures (RMMs) could have on reducing losses from hurricanes and earthquakes as well as improving the solvency position of insurers who provide coverage against these hazards. We first explore why relatively few individuals adopt cost-effective RMMs by reporting on the results of empirical studies and controlled laboratory studies. We then investigate the impact that an RMM has on both the expected losses and those from a worst case scenario in two model cities—Oakland (an earthquake-prone area) and Miami/Dade County (a hurricane-prone area) which were constructed respectively with the assistance of two modeling firms. The paper then explores three programs for forging a meaningful public-private sector partnership: well-enforced building codes, insurance premium reductions linked with long-term loans, and lower deductibles on insurance policies tied to mitigation. We conclude by briefly examining four issues for future research on linking mitigation with insurance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007097906602
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  • 106
    Electronic Resource
    Electronic Resource
    Human Interindividual Variability in Parameters Related to Health Risks (1999)
    Springer
    Risk analysis 19 (1999), S. 711-726 
    Details
    ISSN: 1539-6924
    Keywords: variability ; exposure ; susceptibility ; risk assessment ; pharmacokinetics ; pharmacodynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This paper reviews existing data on the variability in parameters relevant for health risk analyses. We cover both exposure-related parameters and parameters related to individual susceptibility to toxicity. The toxicity/susceptibility data base under construction is part of a longer term research effort to lay the groundwork for quantitative distributional analyses of non-cancer toxic risks. These data are broken down into a variety of parameter types that encompass different portions of the pathway from external exposure to the production of biological responses. The discrete steps in this pathway, as we now conceive them, are: •Contact Rate (Breathing rates per body weight; fish consumption per body weight) •Uptake or Absorption as a Fraction of Intake or Contact Rate •General Systemic Availability Net of First Pass Elimination and Dilution via Distribution Volume (e.g., initial blood concentration per mg/kg of uptake) •Systemic Elimination (half life or clearance) •Active Site Concentration per Systemic Blood or Plasma Concentration •Physiological Parameter Change per Active Site Concentration (expressed as the dose required to make a given percentage change in different people, or the dose required to achieve some proportion of an individual's maximum response to the drug or toxicant) •Functional Reserve Capacity–Change in Baseline Physiological Parameter Needed to Produce a Biological Response or Pass a Criterion of Abnormal Function Comparison of the amounts of variability observed for the different parameter types suggests that appreciable variability is associated with the final step in the process–differences among people in “functional reserve capacity.” This has the implication that relevant information for estimating effective toxic susceptibility distributions may be gleaned by direct studies of the population distributions of key physiological parameters in people that are not exposed to the environmental and occupational toxicants that are thought to perturb those parameters. This is illustrated with some recent observations of the population distributions of Low Density Lipoprotein Cholesterol from the second and third National Health and Nutrition Examination Surveys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007045922532
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  • 107
    Electronic Resource
    Electronic Resource
    A Perspective on Nuclear Waste (1999)
    Springer
    Risk analysis 19 (1999), S. 751-758 
    Details
    ISSN: 1539-6924
    Keywords: nuclear waste ; high-level waste ; performance assessment ; Yucca Mountain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The management of spent nuclear fuel and high-level nuclear waste has the deserved reputation as one of the most intractable policy issues facing the United States and other nations using nuclear reactors for electric power generation. This paper presents the author's perspective on this complex issue, based on a decade of service with the Nuclear Waste Technical Review Board and Board on Radioactive Waste Management of the National Research Council.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007002107511
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  • 108
    Electronic Resource
    Electronic Resource
    Historical Relationship Between Performance Assessment for Radioactive Waste Disposal and Other Types of Risk Assessment (1999)
    Springer
    Risk analysis 19 (1999), S. 763-807 
    Details
    ISSN: 1539-6924
    Keywords: risk assessment ; probabilistic risk assessment ; performance assessment ; policy analysis ; history of technology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This article describes the evolution of the process for assessing the hazards of a geologic disposal system for radioactive waste and, similarly, nuclear power reactors, and the relationship of this process with other assessments of risk, particularly assessments of hazards from manufactured carcinogenic chemicals during use and disposal. This perspective reviews the common history of scientific concepts for risk assessment developed until the 1950s. Computational tools and techniques developed in the late 1950s and early 1960s to analyze the reliability of nuclear weapon delivery systems were adopted in the early 1970s for probabilistic risk assessment of nuclear power reactors, a technology for which behavior was unknown. In turn, these analyses became an important foundation for performance assessment of nuclear waste disposal in the late 1970s. The evaluation of risk to human health and the environment from chemical hazards is built on methods for assessing the dose response of radionuclides in the 1950s. Despite a shared background, however, societal events, often in the form of legislation, have affected the development path for risk assessment for human health, producing dissimilarities between these risk assessments and those for nuclear facilities. An important difference is the regulator's interest in accounting for uncertainty.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007058325258
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  • 109
    Electronic Resource
    Electronic Resource
    Development of a Performance Assessment Capability in the Waste Management Programs of the U.S. Nuclear Regulatory Commission (1999)
    Springer
    Risk analysis 19 (1999), S. 847-876 
    Details
    ISSN: 1539-6924
    Keywords: performance assessment ; nuclear waste ; risk-informed regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The U.S. Nuclear Regulatory Commission (NRC) staff has developed a performance assessment capability to address three programmatic areas in nuclear waste management: high-level waste, low-level waste, and decommissioning of licensed facilities (license termination). The NRC capability consists of: (1) methodologies for performance assessment; (2) models and computer codes for estimating system performance; (3) regulatory guidance in various forms, such as regulations, Branch Technical Positions, and Standard Review Plans; and (4) a technical staff experienced in executing and evaluating performance assessments for a variety of waste systems. Although the tools and techniques are refined for each programmatic area, general approaches and similar issues are encountered in all areas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007062426166
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  • 110
    Electronic Resource
    Electronic Resource
    A Decision Theory Perspective on the Disposal of High-Level Radioactive Waste (1999)
    Springer
    Risk analysis 19 (1999), S. 903-913 
    Details
    ISSN: 1539-6924
    Keywords: nuclear waste ; performance assessment ; Yucca Mountain ; probability ; repository ; high-level waste ; risk ; engineered barriers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract In this paper the problem of high-level nuclear waste disposal is viewed as a five-stage, cascaded decision problem. The first four of these decisions having essentially been made, the work of recent years has been focused on the fifth stage, which concerns specifics of the repository design. The probabilistic performance assessment (PPA) work is viewed as the outcome prediction for this stage, and the site characterization work as the information gathering option. This brief examination of the proposed Yucca Mountain repository through a decision analysis framework resulted in three conclusions: (1) A decision theory approach to the process of selecting and characterizing Yucca Mountain would enhance public understanding of the issues and solutions to high-level waste management; (2) engineered systems are an attractive alternative to offset uncertainties in the containment capability of the natural setting and should receive greater emphasis in the design of the repository; and (3) a strategy of “waste management” should be adopted, as opposed to “waste disposal,” as it allows for incremental confirmation and confidence building of a permanent solution to the high-level waste problem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007066527075
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  • 111
    Electronic Resource
    Electronic Resource
    Total System Performance Assessment for Waste Disposal Using a Logic Tree Approach (1999)
    Springer
    Risk analysis 19 (1999), S. 915-931 
    Details
    ISSN: 1539-6924
    Keywords: Yucca Mountain ; performance assessment ; logic tree ; high-level radioactive waste ; Monte Carlo ; expert judgment ; repository ; groundwater ; climate ; infiltration ; percolation ; hydrothermal ; corrosion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The Electric Power Research Institute (EPRI) has sponsored the development of a model to assess the long-term, overall “performance” of the candidate spent fuel and high-level radioactive waste (HLW) disposal facility at Yucca Mountain, Nevada. The model simulates the processes that lead to HLW container corrosion, HLW mobilization from the spent fuel, and transport by groundwater, and contaminated groundwater usage by future hypothetical individuals leading to radiation doses to those individuals. The model must incorporate a multitude of complex, coupled processes across a variety of technical disciplines. Furthermore, because of the very long time frames involved in the modeling effort (≫104 years), the relative lack of directly applicable data, and many uncertainties and variabilities in those data, a probabilistic approach to model development was necessary. The developers of the model chose a logic tree approach to represent uncertainties in both conceptual models and model parameter values. The developers felt the logic tree approach was the most appropriate. This paper discusses the value and use of logic trees applied to assessing the uncertainties in HLW disposal, the components of the model, and a few of the results of that model. The paper concludes with a comparison of logic trees and Monte Carlo approaches.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007018611145
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  • 112
    Electronic Resource
    Electronic Resource
    Comments on the Legal Admissibility of a Performance Assessment for a Radioactive Waste Disposal Facility (1999)
    Springer
    Risk analysis 19 (1999), S. 991-993 
    Details
    ISSN: 1539-6924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007078829801
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  • 113
    Electronic Resource
    Electronic Resource
    Performance Assessments of Nuclear Waste Repositories: A Dialogue on Their Value and Limitations (1999)
    Springer
    Risk analysis 19 (1999), S. 933-958 
    Details
    ISSN: 1539-6924
    Keywords: compliance certification application ; engineering analysis ; geochemistry ; geohydrology ; performance assessment ; probabilistic systems analysis ; radioactive waste ; scientific validity ; uncertainty ; 40 CFR 191
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Performance Assessment (PA) is the use of mathematical models to simulate the long-term behavior of engineered and geologic barriers in a nuclear waste repository; methods of uncertainty analysis are used to assess effects of parametric and conceptual uncertainties associated with the model system upon the uncertainty in outcomes of the simulation. PA is required by the U.S. Environmental Protection Agency as part of its certification process for geologic repositories for nuclear waste. This paper is a dialogue to explore the value and limitations of PA. Two “skeptics” acknowledge the utility of PA in organizing the scientific investigations that are necessary for confident siting and licensing of a repository; however, they maintain that the PA process, at least as it is currently implemented, is an essentially unscientific process with shortcomings that may provide results of limited use in evaluating actual effects on public health and safety. Conceptual uncertainties in a PA analysis can be so great that results can be confidently applied only over short time ranges, the antithesis of the purpose behind long-term, geologic disposal. Two “proponents” of PA agree that performance assessment is unscientific, but only in the sense that PA is an engineering analysis that uses existing scientific knowledge to support public policy decisions, rather than an investigation intended to increase fundamental knowledge of nature; PA has different goals and constraints than a typical scientific study. The “proponents” describe an ideal, six-step process for conducting generalized PA, here called probabilistic systems analysis (PSA); they note that virtually all scientific content of a PA is introduced during the model-building steps of a PSA; they contend that a PA based on simple but scientifically acceptable mathematical models can provide useful and objective input to regulatory decision makers. The value of the results of any PA must lie between these two views and will depend on the level of knowledge of the site, the degree to which models capture actual physical and chemical processes, the time over which extrapolations are made, and the proper evaluation of health risks attending implementation of the repository. The challenge is in evaluating whether the quality of the PA matches the needs of decision makers charged with protecting the health and safety of the public.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007070627983
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  • 114
    Electronic Resource
    Electronic Resource
    Resolution of the Long-Term Performance Issues at the Waste Isolation Pilot Plant (1999)
    Springer
    Risk analysis 19 (1999), S. 1003-1016 
    Details
    ISSN: 1539-6924
    Keywords: WIPP ; radioactive waste ; repository ; performance assessment ; transuranic waste
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The Waste Isolation Pilot Plant (WIPP) is a geological repository for disposal of U.S. defense transuranic radioactive waste. Built and operated by the U.S. Department of Energy (DOE), it is located in the Permian age salt beds in southeastern New Mexico at a depth of 655 m. Performance assessment for the repository's compliance with the 10,000-year containment standards was completed in 1996 and the U.S. Environmental Protection Agency (EPA) certified in 1998 that the repository meets compliance with the EPA standards 40 CFR 191 and 40 CFR 194. The Environmental Evaluation Group (EEG) review of the DOE's application for certification identified a number of issues. These related to the scenarios, conceptual models, and values of the input parameters used in the calculations. It is expected that these issues will be addressed and resolved during the first 5-year recertification process that began with the first receipt of waste at WIPP on March 26, 1999, and scheduled to be completed in March 2004.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007082930709
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  • 115
    Electronic Resource
    Electronic Resource
    Risk Perception in Context: The Savannah River Site Stakeholder Study (1999)
    Springer
    Risk analysis 19 (1999), S. 1019-1035 
    Details
    ISSN: 1539-6924
    Keywords: risk perception ; CRESP ; trust ; DOE Savannah River site ; risk assessment ; stakeholder ; economic dependence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Environmental managers are increasingly charged with involving the public in the development and modification of policies regarding risks to human health and the environment. Involving the public in environmental decision making first requires a broad understanding of how and why the public perceives various risks. The Savannah River Stakeholder Study was conducted with the purpose of investigating individual, economic, and social characteristics of risk perceptions among those living near the Savannah River Nuclear Weapons Site. A number of factors were found to impact risk perceptions among those living near the site. One's estimated proximity to the site and relative river location surfaced as strong determinants of risk perceptions among SRS residents. Additionally, living in a quality neighborhood and demonstrating a willingness to accept health risks for economic gain strongly abated heightened risk perceptions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007095808381
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  • 116
    Electronic Resource
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    Quantifying Uncertainty in a Risk Assessment Using Human Data (1999)
    Springer
    Risk analysis 19 (1999), S. 1077-1090 
    Details
    ISSN: 1539-6924
    Keywords: risk assessment ; uncertainty ; formaldehyde ; decision analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A call for risk assessment approaches that better characterize and quantify uncertainty has been made by the scientific and regulatory community. This paper responds to that call by demonstrating a distributional approach that draws upon human data to derive potency estimates and to identify and quantify important sources of uncertainty. The approach is rooted in the science of decision analysis and employs an influence diagram, a decision tree, probabilistic weights, and a distribution of point estimates of carcinogenic potency. Its results estimate the likelihood of different carcinogenic risks (potencies) for a chemical under a specific scenario. For this exercise, human data on formaldehyde were employed to demonstrate the approach. Sensitivity analyses were performed to determine the relative impact of specific levels and alternatives on the potency distribution. The resulting potency estimates are compared with the results of an exercise using animal data on formaldehyde. The paper demonstrates that distributional risk assessment is readily adapted to situations in which epidemiologic data serve as the basis for potency estimates. Strengths and weaknesses of the distributional approach are discussed. Areas for further application and research are recommended.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007026510198
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  • 117
    Electronic Resource
    Electronic Resource
    Adaptive Spatial Sampling of Contaminated Soil (1999)
    Springer
    Risk analysis 19 (1999), S. 1059-1069 
    Details
    ISSN: 1539-6924
    Keywords: spatial statistics ; optimal sequential search ; adaptive sampling ; simulation-optimization ; multiple imputation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Suppose that a residential neighborhood may have been contaminated by a nearby abandoned hazardous waste site. The suspected contamination consists of elevated soil concentrations of chemicals that are also found in the absence of site-related contamination. How should a risk manager decide which residential properties to sample and which ones to clean? This paper introduces an adaptive spatial sampling approach which uses initial observations to guide subsequent search. Unlike some recent model-based spatial data analysis methods, it does not require any specific statistical model for the spatial distribution of hazards, but instead constructs an increasingly accurate nonparametric approximation to it as sampling proceeds. Possible cost-effective sampling and cleanup decision rules are described by decision parameters such as the number of randomly selected locations used to initialize the process, the number of highest-concentration locations searched around, the number of samples taken at each location, a stopping rule, and a remediation action threshold. These decision parameters are optimized by simulating the performance of each decision rule. The simulation is performed using the data collected so far to impute multiple probable values of unknown soil concentration distributions during each simulation run. This optimized adaptive spatial sampling technique has been applied to real data using error probabilities for wrongly cleaning or wrongly failing to clean each location (compared to the action that would be taken if perfect information were available) as evaluation criteria. It provides a practical approach for quantifying trade-offs between these different types of errors and expected cost. It also identifies strategies that are undominated with respect to all of these criteria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007022409290
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  • 118
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    Stringency of Workplace Air Contaminant Exposure Limits: A Case Study of OSHA Risk Management (1999)
    Springer
    Risk analysis 19 (1999), S. 1113-1125 
    Details
    ISSN: 1539-6924
    Keywords: OSHA ; environmental health regulation ; risk ambiguity ; indoor/workplace air quality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Political context may play a large role in influencing the efficiency of environmental and health regulations. This case study uses data from a 1989 update of the Occupational Safety and Health Administration (OSHA) Permissible Exposure Limits (PELs) program to determine the relative effects of legislative mandates, costly acquisition of information by the agency, and pressure applied by special interest groups upon exposure standards. The empirical analysis suggests that federal agencies successfully thwart legislative attempts to limit agency discretion, and that agencies exercise bounded rationality by placing greater emphasis on more easily obtained information. The 1989 PELs were less significantly related to more costly information, contained “safety factors” for chemicals presenting relatively more ambiguous risks, and the proposed standard stringencies showed evidence of being influenced by vying industry and labor interests.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007082627945
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  • 119
    Electronic Resource
    Electronic Resource
    Cancer Dose-Response Modeling of Epidemiological Data on Worker Exposures to Aldrin and Dieldrin (1999)
    Springer
    Risk analysis 19 (1999), S. 1101-1111 
    Details
    ISSN: 1539-6924
    Keywords: aldrin ; dieldrin ; epidemiology ; occupational exposure ; cancer dose-response modeling ; proportional hazards ; hormesis ; distributional characterizations of added cancer risk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The paper applies classical statistical principles to yield new tools for risk assessment and makes new use of epidemiological data for human risk assessment. An extensive clinical and epidemiological study of workers engaged in the manufacturing and formulation of aldrin and dieldrin provides occupational hygiene and biological monitoring data on individual exposures over the years of employment and provides unusually accurate measures of individual lifetime average daily doses. In the cancer dose-response modeling, each worker is treated as a separate experimental unit with his own unique dose. Maximum likelihood estimates of added cancer risk are calculated for multistage, multistage-Weibull, and proportional hazards models. Distributional characterizations of added cancer risk are based on bootstrap and relative likelihood techniques. The cancer mortality data on these male workers suggest that low-dose exposures to aldrin and dieldrin do not significantly increase human cancer risk and may even decrease the human hazard rate for all types of cancer combined at low doses (e.g., 1 μg/kg/day). The apparent hormetic effect in the best fitting dose-response models for this data set is statistically significant. The decrease in cancer risk at low doses of aldrin and dieldrin is in sharp contrast to the U.S. Environmental Protection Agency's upper bound on cancer potency based on mouse liver tumors. The EPA's upper bound implies that lifetime average daily doses of 0.0000625 and 0.00625 μg/kg body weight/day would correspond to increased cancer risks of 0.000001 and 0.0001, respectively. However, the best estimate from the Pernis epidemiological data is that there is no increase in cancer risk in these workers at these doses or even at doses as large as 2 μg/kg/day.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007030611107
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  • 120
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    Vehicle Emission Unit Risk Factors for Transportation Risk Assessments (1999)
    Springer
    Risk analysis 19 (1999), S. 1157-1171 
    Details
    ISSN: 1539-6924
    Keywords: risk assessment ; transportation risk ; diesel exhaust ; fugitive dust ; vehicle emissions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract When the transportation risk posed by shipments of hazardous chemical and radioactive materials is being assessed, it is necessary to evaluate the risks associated with both vehicle emissions and cargo-related risks. Diesel exhaust and fugitive dust emissions from vehicles transporting hazardous shipments lead to increased air pollution, which increases the risk of latent fatalities in the affected population along the transport route. The estimated risk from these vehicle-related sources can often be as large or larger than the estimated risk associated with the material being transported. In this paper, data from the U.S. Environmental Protection Agency's Motor Vehicle-Related Air Toxics Study are first used to develop latent cancer fatality estimates per kilometer of travel in rural and urban areas for all diesel truck classes. These unit risk factors are based on studies investigating the carcinogenic nature of diesel exhaust. With the same methodology, the current per-kilometer latent fatality risk factor used in transportation risk assessments for heavy diesel trucks in urban areas is revised and the analysis expanded to provide risk factors for rural areas and all diesel truck classes. These latter fatality estimates may include, but are not limited to, cancer fatalities and are based primarily on the most recent epidemiological data available on mortality rates associated with ambient air PM-10 concentrations.
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    URL: http://dx.doi.org/10.1023/A:1007038812924
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    Monte Carlo Sensitivity Analysis of Unknown Parameters in Hazardous Materials Transportation Risk Assessment (1999)
    Springer
    Risk analysis 19 (1999), S. 1173-1184 
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    ISSN: 1539-6924
    Keywords: transportation risk ; Hydraxine ; sensitivity analysis ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The US Department of Transportation was interested in the risks associated with transporting Hydrazine in tanks with and without relief devices. Hydrazine is both highly toxic and flammable, as well as corrosive. Consequently, there was a conflict as to whether a relief device should be used or not. Data were not available on the impact of relief devices on release probabilities or the impact of Hydrazine on the likelihood of fires and explosions. In this paper, a Monte Carlo sensitivity analysis of the unknown parameters was used to assess the risks associated with highway transport of Hydrazine. To help determine whether or not relief devices should be used, fault trees and event trees were used to model the sequences of events that could lead to adverse consequences during transport of Hydrazine. The event probabilities in the event trees were derived as functions of the parameters whose effects were not known. The impacts of these parameters on the risk of toxic exposures, fires, and explosions were analyzed through a Monte Carlo sensitivity analysis and analyzed statistically through an analysis of variance. The analysis allowed the determination of which of the unknown parameters had a significant impact on the risks. It also provided the necessary support to a critical transportation decision even though the values of several key parameters were not known.
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    URL: http://dx.doi.org/10.1023/A:1007090829762
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    On Modeling Correlated Random Variables in Risk Assessment (1999)
    Springer
    Risk analysis 19 (1999), S. 1205-1214 
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    ISSN: 1539-6924
    Keywords: Monte Carlo ; correlation ; copulas ; bivariate distributions ; dioxins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Monte Carlo methods in risk assessment are finding increasingly widespread application. With the recognition that inputs may be correlated, the incorporation of such correlations into the simulation has become important. Most implementations rely upon the method of Iman and Conover for generating correlated random variables. In this work, alternative methods using copulas are presented for deriving correlated random variables. It is further shown that the particular algorithm or assumption used may have a substantial effect on the output results, due to differences in higher order bivariate moments.
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    URL: http://dx.doi.org/10.1023/A:1007047014741
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    Health Risk Assessment of a Modern Municipal Waste Incinerator (1999)
    Springer
    Risk analysis 19 (1999), S. 1215-1222 
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    ISSN: 1539-6924
    Keywords: municipal waste incineration ; risk assessment ; Monte-Carlo simulation ; time activity patterns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract During the modernization of the municipal waste incinerator (MWI, maximum capacity of 180,000 tons per year) of Metropolitan Grenoble (405,000 inhabitants), in France, a risk assessment was conducted, based on four tracer pollutants: two volatile organic compounds (benzene and 1, 1, 1 trichloroethane) and two heavy metals (nickel and cadmium, measured in particles). A Gaussian plume dispersion model, applied to maximum emissions measured at the MWI stacks, was used to estimate the distribution of these pollutants in the atmosphere throughout the metropolitan area. A random sample telephone survey (570 subjects) gathered data on time-activity patterns, according to demographic characteristics of the population. Life-long exposure was assessed as a time-weighted average of ambient air concentrations. Inhalation alone was considered because, in the Grenoble urban setting, other routes of exposure are not likely. A Monte Carlo simulation was used to describe probability distributions of exposures and risks. The median of the life-long personal exposures distribution to MWI benzene was 3.2·10−5 μg/m3 (20th and 80th percentiles = 1.5·10−5 and 6.5·10−5 μg/m3), yielding a 2.6·10−10 carcinogenic risk (1.2·10−10–5.4·10−10). For nickel, the corresponding life-time exposure and cancer risk were 1.8·10−4 μg/m3 (0.9.10−4 – 3.6·10−4 μg/m3) and 8.6·10−8 (4.3·10−8–17.3·10−8); for cadmium they were respectively 8.3·10−6 μg/m3 (4.0·10−6–17.6·10−6) and 1.5·10−8 (7.2·10−9–3.1·10−8). Inhalation exposure to cadmium emitted by the MWI represented less than 1% of the WHO Air Quality Guideline (5 ng/m3), while there was a margin of exposure of more than 109 between the NOAEL (150 ppm) and exposure estimates to trichloroethane. Neither dioxins nor mercury, a volatile metal, were measured. This could lessen the attributable life-long risks estimated. The minute (VOCs and cadmium) to moderate (nickel) exposure and risk estimates are in accord with other studies on modern MWIs meeting recent emission regulations, however.
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    Risk-Based Assessment of Soil and Groundwater Quality in the Netherlands: Standards and Remediation Urgency (1999)
    Springer
    Risk analysis 19 (1999), S. 1235-1249 
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    ISSN: 1539-6924
    Keywords: soil contamination ; remediation urgency ; standards ; human exposure ; ecotoxicological risks ; risk due to contaminant migration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract To assess soil and groundwater quality two generic (i.e. multifunctional) risk-based standards, Target and Intervention Value, have been developed, in the framework of the Dutch Soil Protection Act. These standards allow soil and groundwater to be classified as clean, slightly contaminated or seriously contaminated. The Target Value is based on potential risks to ecosystems, while the Intervention Value is based on potential risks to humans and ecosystems. In the case of serious soil contamination the site has, in principle, to be remediated, making it necessary to determine the remediation urgency on the basis of actual (i.e. site-specific) risks to humans and ecosystems and, besides, actual risks due to contaminant migration.
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    URL: http://dx.doi.org/10.1023/A:1007003332488
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    Neuronal growth via hybrid system of self-growing and diffusion based grammar rules: I (1995)
    Springer
    Bulletin of mathematical biology 57 (1995), S. 205-227 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The formation of neuronal networks requires axonal growth towards target neutons. A simple set of grammar rules is introduced to describe axonal growth towards target cells situated both at short and long distances from the growing neuron. Growth for short distances is descrbed by growth following the highest gradient of a chemical compound (which is spread by diffusion from the targets). This approach fails to describe long-distance growth, which is addressed by adopting a graph grammar theory for growing trees. With these rules a flexible tool to draw network of neurons by computer can be developed.
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    Interlocking triads of growth control in tumors (1995)
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    Bulletin of mathematical biology 57 (1995), S. 345-366 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A pair of growth control triads are used to describe coincident tumor growth and liver regeneration after partial hepatectomy. The models are extensions of previous growth control models which describe tumor growth in an unperturbed host (Michelson and Leith, 1991,Bull. math. Biol. 53, 639–656; idem, 1992, Proceedings of the Third International Conference on Communications and Control, Vol. 2, pp. 481–490; idem, 1992,Bull. math. Biol. 55, 993–1011; idem,J. theor. Biol. 169, 327–338). The linkage between the two triads depends upon systemic signals carried by soluble factors, and mathematical descriptors based upon biological first principals are proposed. The sources of the growth factors, their targets and the processing of their signals are investigated. Analyses of equilibrium in the constant coefficients case and simulated growth curves for the dynamic system are presented, and the effects of growth factor-induced mitogenesis and angiogenesis are discussed in particular. A case is made for early and late responses in the coupled control system. The biology of the signal processing paradigm is placed within a new theoretical context and discussed with regard to tumor adaptation, liver differentiation and the development of a tumor hypoxic fraction.
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    Optimal population stabilization and control using the Leslie matrix model (1995)
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    Bulletin of mathematical biology 57 (1995), S. 381-399 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract We consider the problem of optimal stabilization and control of populations which follow the Leslie model dynamics, within state space and control systems theory and methodology. Various types of culling strategies are formulated and introduced into the Leslie model as control inputs, and their effect on global asymptotic stability is investigated. Our new approach provides answers to several unexplored problems. We show that in general it is possible to achieve a desired stable equilibrium population level, through the design of a class ofshifted-proportional stabilizing culling policies. Further, we formulate general non-linear constrained opitmization problems, for obtaining the cost-optimal policy among this generally infinite class of such stabilizing policies. The theoretical findings are illustrated through the solution of the problem over an infinite planning horizon for a numerical example. A comparative study of the costs and dynamic effects of various culling strategies also supports the mathematical results.
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    A data assimilation technique applied to a predator-prey model (1995)
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    Bulletin of mathematical biology 57 (1995), S. 593-617 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A new approach for data assimilation, which is based on the adjoint method, but allows the computer code for the adjoint to be constructed directly from the model computer code, is described. This technique is straightforward and reduces the chance of introducing errors in the construction of the adjoint code. Implementation of the technique is illustrated by applying it to a simple predator-prey model in a model fitting mode. A series of identical twin numerical experiments are used to show that this data assimilation approach can successfully recover model parameters as well as initial conditions. However, the ease with which these values are recovered is dependent on the form of the model equations as well as on the type and amount of data that are available. Additional numerical experiments show that sufficient coefficient and parameter recoveries are possible even when the assimilated data contain significant random noise. Thus, for biological systems that can be described by ecosystem models, the adjoint method represents a powerful approach for estimating values for little-known biological parameters, such as initial conditions, growth rates, and mortality rates.
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    Building activity and longevity of queenless groups of the Oriental hornet,Vespa orientalis (1995)
    Springer
    Bulletin of mathematical biology 57 (1995), S. 441-460 
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    ISSN: 1522-9602
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    Topics: Biology , Mathematics
    Notes: Abstract The effect of group size on behavioral parameters of the Oriental hornet,Vespa orientalis, was assessed experimentally under laboratory conditions. Hornet groups of various sizes (ranging from 1 to 100 individuals per group) comprised of young individuals (0–24 hr of age) devoid of a queen were placed in artificial breeding boxes (ABBs). The following three quantitative parameters were evaluated: the amount and rate of building as a function of the number of hornets in the group, the rate of oviposition as, related to group size and the longevity of hornets as a function of their group size. The probability for the occurrence of these events was similarly considered and additional behavioral parameters were only assessed qualitatively. Results of this investigation revealed a relation between the three mentioned quantitative behavioral parameters and the number of hornets per group. The number of hornets per group was positively related to the extent of building, the number of cells built by a group is $$2\pi \sqrt {group size} $$ , but negatively related to the rate of building. As for the delay of building, a non-monotone relation was found. The relation between number of hornets per group and the oviposition delay was found to be non-monotone; the number of hornets per group and their longevity were found to be inversely related. Discrepanices were recorded on the very small (1–2 individuals) or very large (100 individuals) hornet groups.
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    Fuzzy classification of nucleotide sequences and bacterial evolution (1995)
    Springer
    Bulletin of mathematical biology 57 (1995), S. 527-537 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A new method for reconstructing evolutionary relationship among bacteria by use of rRNA sequence data is proposed. The method is based on the concept of fuzzy classification of probabilitiesp(i), p(i/j) andp(i/j*) (i=A,G,C,U) of each sequence. The resulting partition tree shares common features of previous works but has some new peculiarities.
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    Book reviews (1995)
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    Bulletin of mathematical biology 57 (1995), S. 619-630 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02460786
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    Gyrotaxis: Interaction between algae and flagellates (1995)
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    Bulletin of mathematical biology 57 (1995), S. 631-650 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract We describe the behaviour of motile microorganisms (e.g. flagellates) attracted by “gyrotaxis” to a sinking, non-motile particle (e.g. an algal cell). The model is based on the application of Stokes' solution for the flow field around the settling cell. The volume within which the flagellate is attracted to the sinking particle is determined from the trajectories of the flagellate. The model of gyrotaxis has several applications; these include the colonization of sinking marine snow particles with motile microoganisms and suspension feeding by protozoa.
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    Effect of dimensionality on Lotka-Volterra predator-prey dynamics: Individual based simulation results (1995)
    Springer
    Bulletin of mathematical biology 57 (1995), S. 507-526 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The effect of varying habitat dimensionality on the dynamics of a model predator-prey system is examined using an individual-based simulation. The general results are that in one dimension fluctuations in abundance of prey and predators occur over a large range of spatial scales (extinctions occur over many spatial scales). In two dimensions (and low mobilities of prey and predators) the dynamics become more predictably periodic at local scales and constant at larger scales due to statistical stabilization. In three dimensions, the model can become “phase-locked” with prey and predators displaying oscillations in abundance over large spatial scales.
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    Dicarboxylic acid fluxes during gluconeogenesis. No channelling of mitochondrial oxalacetate (1995)
    Springer
    Bulletin of mathematical biology 57 (1995), S. 557-568 
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    Topics: Biology , Mathematics
    Notes: Abstract A rather complete model of the gluconeogenic pathway was used, with the known separate pools of mitochondrial and cytosolic oxalacetate, malate and aspartate. The fumarase, malate dehydrogenase and glutamate oxalacetate transaminase reactions were assumed to be isotopically actively reversible, but none at isotopic equilibrium. Malate was assumed to exchange actively between the mitochondrial and cytosol, while aspartate exchange was more limited, in agreement with the known electrogenic nature of aspartate export from the mitochondria. This model was fit to14C data obtained in hepatocyte studies, and to the whole rat14C data obtained by Heath and Rose (Biochem J. 227, 851–876, 1985). The latter data were easily fit to our model, when a single mitochondrial oxalacetate pool was assumed. However, invoking two mitochondrial oxalacetate pools, as proposed by Heath and Rose, with the oxalacetate formed via pyruvate carboxylase preferentially channelled to gluconeogenesis, could not be fit with the known differences in scrambling in glucose and glutamate produced from L[3-14C]lactate.
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    Mathematical analysis of a proposed mechanism for oscillatory insulin secretion in perifused HIT-15 cells (1995)
    Springer
    Bulletin of mathematical biology 57 (1995), S. 569-591 
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    ISSN: 1522-9602
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    Topics: Biology , Mathematics
    Notes: Abstract Oscillatory secretion of insulin has been observed in many different experimental preparations ranging from pancreatic islets to the whole pancreas. Here we examine the mathematical features underlying a possible model for oscillatory secretion from the perifused, insulin-secreting cell line, HIT-15. The model includes the kinetics of uptake of glucose by GLUT transporters, the rate of glucose metabolism within the cell, and the effect of glucose on the rate of insulin secretion. Putative feedback by insulin on the rate of glucose transport into the cells is treated phenomenologically and leads to insulin oscillations similar to those observed experimentally in HIT cells. The resulting set of ordinary differential equations is simplified by time-scale analysis to a two-variable set of ordinary differential equations. Because of this simplification we can explore, in great detail, the characteristics of the oscillations and their sensitivity to parameter variation using phase plane analysis.
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    Sperm motility in the presence of boundaries (1995)
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    Bulletin of mathematical biology 57 (1995), S. 679-699 
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    Topics: Biology , Mathematics
    Notes: Abstract The fluid dynamics of sperm motility near both rigid and elastic walls is studied using the immersed boundary method. Simulations of both single and interacting organisms are presented. In particular, we find that nearby organisms originally undulating with a 90° phase shift may adjust their relative swimming velocities and phase-lock. Comparisons with previous analytical results are also discussed. The tendency of a near-wall to attract organisms is demonstrated.
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    Contributions of memory B cells to secondary immune response (1995)
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    Bulletin of mathematical biology 57 (1995), S. 713-731 
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    ISSN: 1522-9602
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    Topics: Biology , Mathematics
    Notes: Abstract The secondary immune response is one of the most important features of immune systems. During the secondary immune response, the immune system can eliminate the antigen, which has been encountered by the individual during the primary invasion, more rapidly and efficiently. Both T and B memory cells contribute to the secondary response. In this paper, we only concentrate on the functions of memory B cells. We explore a model describing the memory contributed by the specific long-lived clone which is maintained by continued stimulation with a small amount of antigens sequestered on the surfaces of the follicular dendritic cells (FDC). The behavior of the secondary response provided by the model can be compared with experimental observations. The model shows that memory B cells indeed play an important role in the secondary response. It is found that a single memory cell in a long-lived clone may not be long-lived. In the present note, the influences of relevant parameters on the secondary response are also explored.
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    Reproduction rate, feeding process, and liebig limitations in cell populations—II (1995)
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    Bulletin of mathematical biology 57 (1995), S. 749-782 
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    ISSN: 1522-9602
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    Topics: Biology , Mathematics
    Notes: Abstract A biological system consisting of a population of cells suspended in a liquid substrate is considered. The general problem addressed in the paper is the derivation of the kinetic pattern of population growth as a statistical effect of a very large number of elementary interactions between a single cell and the molecules of nutrient in substrate. Solution of the problem is obtained in the form of equation expressing the population growth ratec as a function of substrate concentration,C s. The analytical expression derived is applied to a real bacterial population (Escherichi coli) and kinetic patterns are theoretically computed. The major findings, expressed roughly, without nuances, are: (i) the concentration of nutrient at the cell membrane,C c, can only be equal to either 0 (for theC s below some threshold valueC *) orC s (forC s〉C *); (ii) the Michaelis-Menten-Monod kinetics observed in experiments is an artifact: the pure (not contaminated by foreign factors) dependence ofc onC s is actually such that the functionc=c(C s) has practically linear increase whenC s〈C *, and is constant,c=c(C *)=const, whenC s〉C *; (iii) the Liebig principle is strictly fulfilled: up to a feasible accuracy of observation, under no circumstances can population growth be limited (controlled) by more than one substrate component—replacement of a limiting component for another one is an instant event rather than a gradual process.
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    Idiotypic regulation of B cell differentiation (1995)
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    Bulletin of mathematical biology 57 (1995), S. 841-881 
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    Notes: Abstract We study the equilibrium properties of idiotypically interacting B cell clones in the case where only the differentiation of B cells is affected by idiotypic interactions. Furthermore, we assume that clones may recognize and be stimulated by self antigen in the same fashion as by antiantibodies. For idiotypically interacting pairs of non-autoreactive clones we observe three qualitatively different dynamical regimes. In the first regime, at small antibody production an antibody-free fixed point, the virgin state, is the only attractor of the system. For intermediate antibody production, a symmetric activated state replaces the virgin state as the only attractor of the system. For large antibody production, finally, the symmetric activated state gives way to two asymmetric activated states where one clone suppresses the other clone. If one or both clones in the pair are autoreactive there is no virgin state. However, we still observe the switch from an almost symmetric activated state to two asymmetric activated states. The two asymmetric activated states at high antibody production have profoundly different implications for a self antigen which is recognized by one of the clones of the pair. In the attractor characterized by high autoantibody concentration the self antigen is attacked vigorously by the immune system while in the opposite steady state the tiny amount of autoantibody hardly affects the self antigen. Accordingly, we call the first state the autoimmune state and the second the tolerant state. In the tolerant state the autoreactive clone is down-regulated by its anti-idiotype providing an efficient mechanism to prevent an autoimmune reaction. However, the antibody production required to achieve this anti-idiotypic control of autoantibodies is rather large.
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    The potassium A-current, low firing rates and rebound excitation in Hodgkin-Huxley models (1995)
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    Bulletin of mathematical biology 57 (1995), S. 899-929 
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    Notes: Abstract It is widely believed, following the work of Connor and Stevens (1971,J. Physiol. Lond. 214, 31–53) that the ability to fire action potentials over a wide frequency range, especially down to very low rates, is due to the transient, potassium A-current (I A). Using a reduction of the classical Hodgkin-Huxley model, we study the effects ofI A on steady firing rate, especially in the near-threshold regime for the onset of firing. A minimum firing rate of zero corresponds to a homoclinic bifurcation of periodic solutions at a critical level of stimulating current. It requires that the membrane's steady-state current-voltage relation be N-shaped rather than monotonic. For experimentally based genericI A parameters, the model does not fire at arbitrarily low rates, although it can for the more atypicalI A parameters given by Connor and Stevens for the crab axon. When theI A inactivation rate is slow, we find that the transient potassium current can mediate more complex firing patterns, such as periodic bursting in some parameter regimes. The number of spikes per burst increases asg A decreases and as inactivation rate decreases. We also study howI A affects properties of transient voltage responses, such as threshold and firing latency for anodal break excitation. We provide mathematical explanations for several of these dynamic behaviors using bifurcation theory and averaging methods.
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    Fractals in science (1995)
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    Bulletin of mathematical biology 57 (1995), S. 939-941 
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    Coping with chaos: Analysis of chaotic data and the exploitation of chaotic systems (1995)
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    Bulletin of mathematical biology 57 (1995), S. 945-946 
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    Book review (1999)
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    Bulletin of mathematical biology 61 (1999), S. 207-208 
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    URL: http://dx.doi.org/10.1006/bulm.1998.0071
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    Modelling the internalization of labelled cells in tumour spheroids (1999)
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    Bulletin of mathematical biology 61 (1999), S. 601-623 
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    Topics: Biology , Mathematics
    Notes: Abstract In this paper a mathematical model is developed to describe the migration of labelled particles within a multicell spheroid. In the model, spatial variations in cell proliferation and death create an internal velocity field which leads to redistribution of the labelled and unlabelled cells. By applying a range of numerical and analytical techniques to the model equations, it is possible to show that, whilst the speed with which the labelled cells migrate through the tumour is independent of the type of cells that are labelled, their limiting distribution depends crucially on whether inert polystyrene microspheres or live tumour cells are labelled. These predictions are shown to be in good qualitative agreement with independent experimental results.
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    URL: http://dx.doi.org/10.1006/bulm.1999.0089
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    Book reviews (1999)
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    Bulletin of mathematical biology 61 (1999), S. 1009-1013 
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    Topics: Biology , Mathematics
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    URL: http://dx.doi.org/10.1006/bulm.1999.0110
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    Modeling the T-cell dynamics and pathogenesis of HTLV-I infection (1999)
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    Bulletin of mathematical biology 61 (1999), S. 935-947 
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    Notes: Abstract Human T-cell lymphotropic virus type I (HTLV-I) infection in humans causes a chronic infection of CD4+ T cells, and is associated with various disease outcomes, among them with the development of adult T-cell leukemia (ATL). The T-cell dynamics after HTLV-I infection can be described in a mathematical model with coupled differential equations. The infection process is modeled assuming cell-to-cell infection of CD4+ T cells. The model allows for CD4+ T cell subsets of susceptible, latently infected and actively infected cells as well as for leukemia cells. Latently infected T cells may harbor the virus for several years until they become activated and able to infect susceptible T cells. Uncontrolled proliferation of CD4+ T cells with monoclonal DNA-integration of HTLV-I results in the development of ATL. The model describes basic features that characterize HTLV-I infection; the chronic infection of CD4+ T cells, the increasing number of abnormal cells and the possible progression to ATL.
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    Size hierarchy and stability in competitive plant populations (1999)
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    Bulletin of mathematical biology 61 (1999), S. 949-961 
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    Notes: Abstract A neighbourhood-based competition model for plant individuals is studied to evaluate how a hierarchical structure related to size may emerge in plant communities. It is shown by numerical simulations and linear stability analysis that many stable states exist in the hierarchical structure when both the total number of individuals and the degree of asymmetry of competition are high. When the hierarchical structures are self-organized by the dynamic instability of the homogeneous state due to non-linearity of competition, it is proved that these states are always locally stable. The relevance of the results to size structures in real plant communities (boreal forests vs tropical and temperate forests) is discussed. This is suggested to be the mechanism responsible for the coexistence of species in plant communities.
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    Comparative dynamics of three models for host-parasitoid interactions in a patchy environment (1999)
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    Bulletin of mathematical biology 61 (1999), S. 141-155 
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    Notes: Abstract Phenomenological models represent a simplified approach to the study of complex systems such as host-parasitoid interactions. In this paper we compare the dynamics of three phenomenological models for host-parasitoid interactions developed by May (1978), May and Hassell (1981) and May et al. (1981). The essence of the paper by May and Hassell (1981) was to define a minimum number of parameters that would describe the interactions, avoiding the technical difficulties encountered when using models that involve many parameters, yet yielding a system of equations that could capture the essence of real world interactions in patchy environments. Those studies dealt primarily with equilibrium and coexistence phenomena. Here we study the dynamics through bifurcation analysis and phase portraits in a much wider range of parameter values, carrying the models beyond equilibrium states. We show that the dynamics can be either stable or chaotic depending on the location of a damping term in the equations. In the case of the stable system, when host density dependence acts first, a stable point is reached, followed by a closed invariant curve in phase space that first increases then decreases, finally returning to an asymptotically stable point. Chaos is not seen. On the other hand, when parasitoid attack occurs before host density dependence, chaos is inevitably apparent. We show, as did May et al. (1981) and stated earlier byWang and Gutierrez (1980), that the sequence of events in host-parasitoid interactions is crucial in determining their stability. In a chaotic state the size of the host (e.g., insect pests) population becomes unpredictable, frequently becoming quite large, a biologically undesirable outcome. From a mathematical point of view the system is of interest because it reveals how a strategically placed damping term can dramatically alter the outcome. Our study, reaching beyond equilibrium states, suggests a strategy for biological control different from that of May et al. (1981).
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    Effects of parasitism over two competing host populations leading to persistence (1999)
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    Bulletin of mathematical biology 61 (1999), S. 179-205 
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    Topics: Biology , Mathematics
    Notes: Abstract In this paper we study the uniform persistence (UP) of an association of two competing host species sharing a directly transmitted macroparasite. Like predators, parasites can regulate UP while the hosts are either coexisting or in a dominance relationship without any infections, but cannot regulate UP in case the hosts are in bistability. The regulatory mechanism depends on the relationships between the parameters, such as host intrinsic growth rate, host carrying capacity, susceptibility, parasite pathogenicity and the magnitude of parasite aggregation. In the case of coexistence the parametric space for UP is more than that for global stability of the host-parasite equilibrium, but is less than that for UP in the case of dominance. In the case of dominance, the parasites can alter the competitive outcome locally or can enhance the local exclusion of the inferior competitor and thus, unlike the predation, parasitism has an beneficial effect over competition. We derive explicitly the range of the values of ratios of the rates of reproduction and survivorship of the hosts, and also of the values of the degree of aggregations, with which macroparasites are not effective in maintaining its beneficial effect over competition. Finally our results support the body-size hypothesis of Price et al. (1988), with possible explanations of certain exceptional examples of the hypothesis.
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    URL: http://dx.doi.org/10.1006/bulm.1998.0087
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    Parametric-equation representation of biconcave erythrocytes (1999)
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    Bulletin of mathematical biology 61 (1999), S. 209-220 
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    Notes: Abstract The representation of the shape of a biconcave erythrocyte by a set of three parametric equations was achieved by using the expressions that transform the curvilinear coordinates from the disc-cyclide coordinate system [denoted J2R; Moon and Spencer (1988), Field Theory Handbook, Springer-Verlag, Berlin] to Cartesian coordinates. The equations are products of elliptic functions, so the challenge was to relate the three major ’shape-defining’ measurements of the human erythrocyte in Cartesian coordinates to three parameters in the new curvilinear coordinates, to give a realistic representation of the shape of the membrane-surface. The relationships between the coefficients of the Cartesian degree-4 surface that describes the discocyte and the coordinate transformation equations were derived with the aid of Mathematica; and the membrane-surface of the cell was drawn using the ParametricPlot3D function in this ‘package’. By having the erythrocyte shape expressed in its new form it is readily amenable to further transformations that might be used to model those changes in shape that are seen when the cells are immersed in media of various osmolalities, or when they change metabolic ’states’. On the other hand, the relationship between the coefficients of the Cartesian expression for the disc-cyclide surface is relevant to image analysis of erythrocytes, as determined by physical methods that rely on Cartesian imaging ’slices’. These methods include confocal microscopy and various nuclear magnetic resonance microimaging procedures.
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    A physical-biological coupled model for algal dynamics in lakes (1999)
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    Bulletin of mathematical biology 61 (1999), S. 239-272 
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    Topics: Biology , Mathematics
    Notes: Abstract A coupled model is presented for simulating physical and biological dynamics in fresh water lakes. The physical model rests upon the assumption that the turbulent kinetic energy in a water column of the lake is fully contained in a mixed layer of variable depth. Below this layer the mechanical energy content is assumed to vanish. Additionally, the horizontal currents are ignored. This one-dimensional two-layered model describes the internal conversion of the mechanical and thermal energy input from the atmosphere into an evolution of the mixed layer depth by entrainment and detrainment mechanisms. It is supposed to form the physical domain in which the simulation of the biological processes takes place. The biological model describes mathematically the typical properties of phyto-and zooplankton, their interactions and their response to the physical environment. This description then allows the study of the behaviour of Lagrangian clusters of virtual plankton that are subjected to such environments. The essence of the model is the dynamical simulation of an arbitrary number of nutrient limited phytoplankton species and one species of zooplankton. The members of the food web above and below affect the model only statically. The model is able to reproduce the typical progression of a predator-prey interaction between phyto-and zooplankton as well as the exploitative competition for nutrients between two phytoplankton species under grazing pressure of Daphnia. It suggests that the influence of the biological system on the physical system results in a weak increase of the surface temperature for coupled simulations, but a considerably higher seasonal thermocline in spring and a lower one in autumn.
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    Zooplankton mortality and the dynamical behaviour of plankton population models (1999)
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    Bulletin of mathematical biology 61 (1999), S. 303-339 
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    Topics: Biology , Mathematics
    Notes: Abstract We investigate the dynamical behaviour of a simple plankton population model, which explicitly simulates the concentrations of nutrient, phytoplankton and zooplankton in the oceanic mixed layer. The model consists of three coupled ordinary differential equations. We use analytical and numerical techniques, focusing on the existence and nature of steady states and unforced oscillations (limit cycles) of the system. The oscillations arise from Hopf bifurcations, which are traced as each parameter in the model is varied across a realistic range. The resulting bifurcation diagrams are compared with those from our previouswork, where zooplankton mortality was simulated by a quadratic function—here we use a linear function, to represent alternative ecological assumptions. Oscillations occur across broader ranges of parameters for the linear mortality function than for the quadratic one, although the two sets of bifurcation diagrams show similar qualitative characteristics. The choice of zooplankton mortality function, or closure term, is an area of current interest in the modelling community, and we relate our results to simulations of other models.
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    Use of Bayes theorem to correct size-specific sampling bias in growth data (1999)
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    Bulletin of mathematical biology 61 (1999), S. 355-363 
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    Notes: Abstract The bayesian decomposition of posterior distribution was used to develop a likelihood function to correct bias in the estimates of population parameters from data collected randomly with size-specific selectivity. Positive distributions with time as a parameter were used for parametrization of growth data. Numerical illustrations are provided. The alternative applications of the likelihood to estimate selectivity parameters are discussed.
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    Probability density functions useful for parametrization of heterogeneity in growth and allometry data (1999)
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    Bulletin of mathematical biology 61 (1999), S. 1015-1016 
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    URL: http://dx.doi.org/10.1006/bulm.1999.0124
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    Pattern formation of scale cells in lepidoptera by differential origin-dependent cell adhesion (1999)
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    Bulletin of mathematical biology 61 (1999), S. 807-828 
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    Notes: Abstract We present a model for the formation of parallel rows of scale cells in the developing adult wing of moths and butterflies. Precursors of scale cells differentiate throughout each epithelial monolayer and migrate into rows that are roughly parallel to the body axis. Grafting experiments have revealed what appears to be a gradient of adhesivity along the wing. What is more, cell adhesivity character is maintained after grafting. Thus we suggest that it is a cell’s location prior to migration that determines its interactions during migration. We use nonlinear bifurcation analysis to show that differential origin-dependent cell adhesion can result in the stabilization of rows over spots.
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    Modeling epithelial cell homeostasis: Steady-state analysis (1999)
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    Bulletin of mathematical biology 61 (1999), S. 1065-1091 
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    Notes: Abstract Critical to epithelial cell viability is the homeostasis of cell volume and composition during changes in transcellular transport. In this study, two previously developed mathematical models (principal cell of the collecting duct and proximal tubule cell) are approximated by their linearizations about a reference condition. This yields matrices which estimate cell volume, cell composition, and transcellular fluxes in response to perturbations of bath conditions and membrane transporter activity. These approximations are themselves extended with the inclusion of linear dependence of membrane transport coefficients on cell variables (e.g., volume, solute concentrations, or electrical potential). This provides cell models with variable permeabilities, which may be homeostatic, and which can be examined systematically: sequentially testing each membrane permeability and its controlling cell variable. In the proximal tubule approximation, volume-mediated increases in peritubular K—Cl or Na—3HCO3 cotransport, and volume-mediated decreases in Na,K-ATPase activity are homeostatic; modulation of peritubular K permeability has little impact. In the principal cell model, volume homeostasis is afforded by volume-sensitive peritubular Na/H exchange or Cl− conductance. Predictions from the linear analysis are confirmed in the full models. This approach yields a systematic examination of homeostasis in an epithelial model, and identifies candidate control parameters.
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    Minimax controller design using rate feedback (1999)
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    Circuits, systems and signal processing 18 (1999), S. 17-25 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A complete analytic characterization and solution construction (done either explicitly or by recursion) for the minimax control problem using optimal rate feedback is given for the case when the plant consists of a known fixed set of coupled oscillators of cardinality not exceeding three. When this is not the case, the problem appears to be analytically intractable, and suboptimal solutions based on numerical techniques are currently the only recourse.
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    Constructing analytical energy functions for lossless network-reduction power system models: Framework and new developments (1999)
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    Circuits, systems and signal processing 18 (1999), S. 1-16 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The task of constructing an energy function is essential for direct stability analysis of electric power systems. This paper presents a general procedure for constructing analytical energy functions for detailed lossless network-reduction power system stability models. This paper primarily (i) develops canonical representations for lossless networkreduction power system models and shows that such canonical representations cover existing stability models, (ii) derives theoretical results regarding the existence of analytical energy functions for the canonical representations, and (iii) presents a systematic procedure to construct corresponding energy functions.
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    Finding all the DC solutions of a certain class of piecewise-linear circuits (1999)
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    Circuits, systems and signal processing 18 (1999), S. 89-110 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The problem of finding all the DC solutions of a certain class of piecewise-linear electronic circuits containing locally passive and locally active one-ports is considered in this paper. An effective method enabling us to locate the solutions is developed. The method constitutes the crucial point of an algorithm based on the idea of successive contraction, division, and elimination that is capable of determining all the solutions. Several numerical examples are given, and some comparison analyses are performed confirming the usefulness of the proposed approach.
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    On Kalman's controllability and observability criteria for singular systems (1999)
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    Circuits, systems and signal processing 18 (1999), S. 269-290 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The controllability and observability properties of a singular system are extensively studied. The definitions of controllability,R-controllability, and impulse controllability are introduced via characteristics of the original state vector. Analogous definitions are presented for the case of observability. The criteria established for controllability and observability are simple rank criteria related to the Markov parameters from the inputs to the states and from the initial conditions to the outputs, respectively. The present results can be considered as the direct extension of Kalman's controllability and observability criteria to the case of singular systems. Finally, the controllability and observability subspaces are derived from the image and the kernel of the controllability and the observability matrices, respectively.
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    Spectral mimicry: A method of synthesizing matching time series with different Fourier spectra (1999)
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    Circuits, systems and signal processing 18 (1999), S. 431-442 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Given a stationary time seriesX and another stationary time seriesY (with a different power spectral density), we describe an algorithm for constructing a stationary time series Z that contains exactly the same values asX permuted in an order such that the power spectral density ofZ closely resembles that ofY. We call this methodspectral mimicry. We prove (under certain restrictions) that, if the univariate cumulative distribution function (CDF) ofX is identical to the CDF ofY, then the power spectral density ofZ equals the power spectral density ofY. We also show, for a class of examples, that when the CDFs ofX andY differ modestly, the power spectral density ofZ closely approximates the power spectral density ofY. The algorithm, developed to design an experiment in microbial population dynamics, has a variety of other applications.
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    On the direction estimation Cramér-Rao bounds in the presence of uncorrelated unknown noise (1999)
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    Circuits, systems and signal processing 18 (1999), S. 479-487 
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    Keywords: Cramér-Rao bounds ; direction-of-arrival estimation ; unknown noise
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The deterministic and stochastic direction estimation Cramér-Rao bounds (CRBs) are studied in the presence of one signal and spatially uncorrelated sensor noise with unknown nonequal variances in array sensors. The explicit CRB expressions are obtained, and their relationship is studied showing some typical properties inherent in the nonidentical noise case.
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    A method for defining analog circuits for the minimization of discrete functionals: An image processing application (1999)
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    Circuits, systems and signal processing 18 (1999), S. 457-477 
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    ISSN: 1531-5878
    Keywords: Nonlinear circuit theory ; co-content ; functional minimization ; image processing
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The solutions of many physical-mathematical problems can be obtained by minimizing proper functionals. In the literature, some methods for the synthesis of analog circuits (mainly cellular neural networks) are presented that find the solution of some of these problems by implementing the discretized Euler-Lagrange equations associated with the pertinent functionals. In this paper, we propose a method for defining analog circuits that directly minimize (in a parallel way) a class of discretized functionals in the frequently occurring case where the solution depends on two spatial variables. The method is a generalization of the one presented in Parodi et al.,Internat. J. Circuit Theory Appl., 26, 477–498, 1998. The analog circuits consist of both a (nonlinear) resistive part and a set of linear capacitors, whose steady-state voltages represent the discrete solution to the problem. The method is based on the potential (co-content) functions associated with voltage-controlled resistive elements. es an example, we describe an application in the field of image processing: the restoration of color images corrupted by additive noise.
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    On Decomposition Theorems for Hardy Spaces on Domains in ℂn and Applications (1995)
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    The journal of Fourier analysis and applications 2 (1995), S. 65-107 
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    Topics: Mathematics
    Notes: Abstract Hardy spaces of analytic functions are studied both on strongly pseudoconvex domains in ℂn and on domains of finite type in ℂ2. Duality theorems, atomic decompositions, and factorization of functions are treated. Mapping properties of certain Hankel operators are studied.
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    Irregular Sampling in Wavelet Subspaces (1995)
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    The journal of Fourier analysis and applications 2 (1995), S. 181-189 
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    Topics: Mathematics
    Notes: Abstract As a particular wavelet subspace, the Paley-Wiener space $B_{\pi}$ has both regular and irregular sampling theorems. A regular sampling theorem in general wavelet subspaces has been established for several years. In this paper, we discuss the irregular sampling problem in wavelet subspaces.
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    Autocorrelation Functions as Translation Invariants in L1 and L2 (1995)
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    The journal of Fourier analysis and applications 2 (1995), S. 217-225 
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    ISSN: 1531-5851
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    Topics: Mathematics
    Notes: Abstract The Adler-Konheim theorem [Proc. Amer. Math. Soc. 13 (1962), 425-428] states that the collection of nth-order autocorrelation functions ${\cal M} = \{M^n(\cdot): n=1,2,\dots\}$ is a complete set of translation invariants for real-valued L1 functions on a locally compact abelian group. It is shown here that there are proper subsets of ${\cal M}$ that also form a complete set of translation invariants, and these subsets are characterized. Specifically, a subset is complete if and only if it contains infinitely many even-order autocorrelation functions. In addition, any infinite subset of $\cal M$ is complete up to a sign. While stated here for functions on $\cal R,$ the proofs presented hold for functions on any locally compact abelian group that is not compact, in particular, on ${\cal R}^n$ and the integer lattice ${\cal Z}^n.$
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    Fourier Inequalities and Moment Subspaces in Weighted Lebesgue Spaces (1995)
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    The journal of Fourier analysis and applications 2 (1995), S. 49-64 
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    Topics: Mathematics
    Notes: Abstract For $k \in {\Bbb N}, k \not= 0,$ define ${\cal F}_kf(\gamma) = \int_{{\Bbb R}^n} f(t)R_k(-2i \pi \gamma.t) \, dt, n\geq 1,$ where $R_k(i\lambda) = e^{i\lambda} - \sum^{k-1}_{j=0} \left(i \lambda \right)^{j} / \left(j~!\right).$ Pointwise estimates and weighted inequalities describing the local Lipschitz continuity of ${\cal F}_kf$ are established. Sufficient conditions are found for the boundedness of ${\cal F}_k$ from $L^p_v$ into $L^q_\mu,$ and a spherical restriction property is proved. A study of the moment subspaces of $L^p_v$ is next developed in the one-variable case, for $1 〈 p 〈 \infty, v$ locally integrable, $v 〉 0$ a.e. It includes a decomposition theorem and a complete classification of all possible sequences of moment subspaces in $L^p_v.$ Characterizations are also given for each class. Applications related to the approximation and decomposition of ${\cal F}_k$ are discussed.
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    Designing Multiresolution Analysis-type Wavelets and Their Fast Algorithms (1995)
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    The journal of Fourier analysis and applications 2 (1995), S. 135-159 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Often, the Dyadic Wavelet Transform is performed and implemented with the Daubechies wavelets, the Battle-Lemarie wavelets, or the splines wavelets, whereas in continuous-time wavelet decomposition a much larger variety of mother wavelets is used. Maintaining the dyadic time-frequency sampling and the recursive pyramidal computational structure, we present various methods for constructing wavelets ψwanted, with some desired shape and properties and which are associated with semi-orthogonal multiresolution analyses. We explain in detail how to design any desired wavelet, starting from any given multiresolution analysis. We also explicitly derive the formulae of the filter bank structure that implements the designed wavelet. We illustrate these wavelet design techniques with examples that we have programmed with Matlab routines.
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    Weil Multipliers (1995)
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    The journal of Fourier analysis and applications 2 (1995), S. 191-215 
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    Topics: Mathematics
    Notes: Abstract This paper studies a class of linear operators on spaces of functions of one real variable, which correspond to multiplication by a measurable function under the Weil transform $\Theta.$ These operators are called Weil multipliers, and arise out of the authors' study of Gabor series and radar ambiguity functions. Representation theory provides a natural class of Weil multipliers: the set of doubly periodic functions with absolutely convergent Fourier series, ${\bf A}({\bf T}^2).$ It will be proved that functions in ${\bf A}({\bf T}^2)$ are $L^p$ multipliers for all $1 \leq p \leq 2$ and, therefore, define bounded linear endomorphisms of ${\bf L}^p({\bf R}).$ Also, we record the fact that the Wiener lemma tells us something about the orbit structure of these multipliers acting on function spaces on the Heisenberg nilmanifold. Linear maps that correspond to multiplication by a function under a unitary conjugacy have a particularly simple spectral decomposition, which yields an approximation theory for these operators and provides insight into the foundation of the authors' previous work on approximate orthonormal bases. Finally, the problem of inversion of a multiplier will be analyzed for smooth functions that have a specified structure near their zeros.
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    URL: http://dx.doi.org/10.1007/s00041-001-4028-1
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    On the Uniqueness in the Inverse Conductivity Problem (1995)
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    The journal of Fourier analysis and applications 2 (1995), S. 227-235 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Let $\Omega$ be a smooth domain in R2 containing a polygon D. The inverse conductivity problem to the the elliptic equation ${\rm div}((1+(k-1)\chi_D)\nabla u)=0\ {\rm in }\ \Omega$ is considered. We show that D is uniquely determined from boundary measurements corresponding two appropriately chosen Neumann datas.
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    A fast transform for spherical harmonics (1999)
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    The journal of Fourier analysis and applications 5 (1999), S. 159-184 
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    ISSN: 1531-5851
    Keywords: Primary 65T20 ; secondary 42C10 ; 33C55 ; spherical harmonics ; fast transforms ; associated Legendre functions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Spherical harmonics arise on the sphere S2 in the same way that the (Fourier) exponential functions {eikθ}k∈ℤ arise on the circle. Spherical harmonic series have many of the same wonderful properties as Fourier series, but have lacked one important thing: a numerically stable fast transform analogous to the Fast Fourier Transform (FFT). Without a fast transform, evaluating (or expanding in) spherical harmonic series on the computer is slow—for large computations probibitively slow. This paper provides a fast transform. For a grid ofO(N2) points on the sphere, a direct calculation has computational complexityO(N4), but a simple separation of variables and FFT reduce it toO(N3) time. Here we present algorithms with timesO(N5/2 log N) andO(N2(log N)2). The problem quickly reduces to the fast application of matrices of associated Legendre functions of certain orders. The essential insight is that although these matrices are dense and oscillatory, locally they can be represented efficiently in trigonometric series.
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    Editorial statement (1999)
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    The journal of Fourier analysis and applications 5 (1999), S. v 
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    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01259370
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    Haar Type Orthonormal Wavelet Bases in R2 (1995)
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    The journal of Fourier analysis and applications 2 (1995), S. 1-14 
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    Topics: Mathematics
    Notes: Abstract K.-H. Grochenig and A. Haas asked whether for every expanding integer matrix A ∈ Mn(ℤ) there is a Haar type orthonormal wavelet basis having dilation factor A and translation lattice ℤn. They proved that this is the case when the dimension n = 1. This article shows that this is also the case when the dimension n = 2.
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    On the Reproducing Formula of Calderon (1995)
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    The journal of Fourier analysis and applications 2 (1995), S. 15-28 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Let $1 〈 p 〈 \infty, h \in L_p ({\Bbb R}),$ and $f \in L_{p^\prime} ({\Bbb R}).$ Under certain conditions on $h,$ we shall prove that $\int_y^\infty (h_t \ast f)(x)\,dt/t$ converges nontangentially to $f(x_0)$ at $(x_0,0)$ for $a.a.\, x_0.$
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    Claude Chevalley (1999)
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    Transformation groups 4 (1999), S. i 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
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    Editorial statement (1999)
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    The journal of Fourier analysis and applications 5 (1999), S. v 
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    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01274185
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    Weakly symmetric spaces and spherical varieties (1999)
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    Transformation groups 4 (1999), S. 3-24 
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    Topics: Mathematics
    Notes: Abstract Weakly symmetric homogeneous spaces were introduced by A. Selberg in 1956. We prove that, for a real reductive algebraic group, they can be characterized as the spaces of real points of affine spherical homogeneous varieties of the complexified group. As an application, under the same assumption on the transitive group, we show that weakly symmetric spaces are precisely the homogeneous Riemannian manifolds with commutative algebra of invariant differential operators.
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    Affine modifications and affine hypersurfaces with a very transitive automorphism group (1999)
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    Transformation groups 4 (1999), S. 53-95 
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    Notes: Abstract We study the modificationA→A′ of an affine domainA which produces another affine domainA′=A[I/f] whereI is a nontrivial ideal ofA andf is a nonzero element ofI. First appeared in passing in the basic paper of O. Zariski [Zar], it was further considered by E. D. Davis [Da]. In [Ka1] its geometric counterpart was applied to construct contractible smooth affine varieties non-isomorphic to Euclidean spaces. Here we provide certain conditions (more general than those in [Ka1]) which guarantee preservation of the topology under a modification. As an application, we show that the group of biregular automorphisms of the affine hypersurfaceX⊂C k+2, given by the equationuv=(p(x 1,...,xk) wherep∈C[x 1,...,x k ],k≥2, actsm-transitively on the smooth part regX ofX for anym∈N. We present examples of such hypersurfaces diffeomorphic to Euclidean spaces.
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    Compactification of symmetric varieties (1999)
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    Transformation groups 4 (1999), S. 273-300 
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    Topics: Mathematics
    Notes: Abstract The symmetric varieties considered in this paper are the quotientsG/H, whereG is an adjoint semi-simple group over a fieldk of characteristic ≠ 2, andH is the fixed point group of an involutorial automorphism ofG which is defined overk. In the casek=C, De Concini and Procesi (1983) constructed a “wonderful” compactification ofG/H. We prove the existence of such a compactification for arbitraryk. We also prove cohomology vanishing results for line bundles on the compactification.
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    Quasi-Hopf twistors for elliptic quantum groups (1999)
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    Transformation groups 4 (1999), S. 303-327 
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    Notes: Abstract The Yang-Baxter equation admits two classes of elliptic solutions, the vertex type and the face type. On the basis of these solutions, two types of elliptic quantum groups have been introduced (Foda et al. [FIJKMY1], Felder [Fe]). Frønsdal [Fr1, Fr2] made a penetrating observation that both of them are quasi-Hopf algebras, obtained by twisting the standard quantum affine algebraU q(g). In this paper we present an explicit formula for the twistors in the form of an infinite product of the universalR matrix ofU q(g). We also prove the shifted cocycle condition for the twistors, thereby completing Frønsdal's findings. This construction entails that, for generic values of the deformation parameters, the representation theory forU q(g) carries over to the elliptic algebras, including such objects as evaluation modules, highest weight modules and vertex operators. In particular, we confirm the conjectures of Foda et al. concerning the elliptic algebraA q,p ( $$\widehat{\mathfrak{s}\mathfrak{l}}_2 $$ ).
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    A convexity theorem for noncommutative gradient flows (1999)
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    Transformation groups 4 (1999), S. 375-404 
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    Topics: Mathematics
    Notes: Abstract In this survey we shall prove a convexity theorem for gradient actions of reductive Lie groups on Riemannian symmetric spaces. After studying general properties of gradient maps, this proof is established by (1) an explicit calculation on the hyperbolic plane followed by a transfer of the results to general reductive Lie groups, (2) a reduction to a problem on abelian spaces using Kostant's Convexity Theorem, (3) an application of Fenchel's Convexity Theorem. In the final section the theorem is applied to gradient actions on other homogeneous spaces and we show, that Hilgert's Convexity Theorem for moment maps can be derived from the results.
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    On the concentrated stochastic likelihood function in array signal processing (1995)
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    Circuits, systems and signal processing 14 (1995), S. 669-674 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The stochastic likelihood function [(STO)LF] associated with the narrowband signal processing problem can be concentrated with respect to the signal covariance matrix elements and the noise power. Although this is a known fact, no clear-cut derivation of the concentrated (STO)LF appears to be available in the literature. In this short paper we provide a simple, complete proof of the concentrated (STO)LF formula.
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    A study of bounds on limit cycles in digital filters (1995)
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    Circuits, systems and signal processing 14 (1995), S. 725-734 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We give bounds on the self-sustained limit cycles in fixed-poin implementations of state-variable-form digital filters having general stable system matrices. These bounds, which are period independent and which concern limit cycles due to quantization errors in physical realizations of digital filters, are given in closed form for second-order sections. A numerical comparison shows that the bounds are smaller than corresponding ones reported in the literature. This is due to our use of real similarity transformations.
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    Reachability of Polynomial Matrix Descriptions (PMDs) (1995)
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    Circuits, systems and signal processing 14 (1995), S. 787-815 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We consider the concept reachability for Polynomial Matrix Descriptions (PMDs); i.e., systems of the form ∑: A(ρ)β(t)=B(ρ)u(t),y(t)=C(ρ)β(t), whereρ:=d/dt the differential operator,A(ρ)=A0+A1 ρ+...+ Av ρ v εR r×r[ρ], AiεR r×r,i=0, 1,..., ν ≥ 1 with rank R A v ≤r B(ρ) =B 0+B 1ρ+...+B σρσ εR r×m[ρ], Bi εR r×m,i=0,1,...,σ ≥ 0 C(ρ)=C0+C1 ρ+...+Cσ1 ρ σ1 εR m1×r[ρ],C i εR m1×r ,i=0, 1,..., σ1 ≥ 0, β(t): (0−, ∞) →R r is the pseudostate of (∑),u(t): [0, ∞) →R m is the control input to (∑), and y(t) is the output of the system (∑). Starting from the fact that generalized state space systems, i.e., systems of the form ∑1: Ex(t)=Ax(t)+ Bu(t), y(t)=Cx(t), whereE εR r×r, rank R E 〈r, A εR r×r,B εR r×m,C εR m1×r represent a particular case of PMDs, we generalize various known results regarding the smooth and impulsive solutions of the homogeneous and the nonhomogeneous system (∑1) to the more general case of PMDs (∑). Relying on the above generalizations we develop a theory regarding the reachability of PMDs using time-domain analysis, which takes into account finite and infinite zeros of the matrix A(s)=L.[A(ρ)]. The present analysis extends in a general way many results previously known only for regular and generalized state space systems.
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    Model conversions of uncertain linear systems using a scaling and squaring geometric series method (1995)
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    Circuits, systems and signal processing 14 (1995), S. 445-463 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper proposes a scaling and squaring geometric series method along with the inverse-geometric series method for finding discrete-time (continuous-time) structured uncertain linear models from continuous-time (discrete-time) structured uncertain linear systems. The above methods allow the use of well-developed theorems and algorithms in the discrete-time (continuous-time) domain to indirectly solve the continuous-time (discretetime) domain problems. Moreover, these methods enhance the flexibility in modeling and control of a hybrid composite system. It has been shown that the commonly used bilinear approximation model is a specific class of the proposed geometric series model.
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    Impulse stress wave propagation in elongated bodies: Apparent deviations from circuit realizability principles (1995)
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    Circuits, systems and signal processing 14 (1995), S. 525-538 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Of concern is the undistorted propagation of pulse stress waves in long thin bodies. The primary signals are arbitrarily sharp pulses projected along thex-axis. It will be seen that these pulses travel close to the speed of sound in unbounded media. Secondary pulses follow representing interactive disturbances traveling along they-axis. But the process brings out certain anomalies in circuit realizability requirements. These issues, transmission parameters, and coupling between the various signals are studied in detail. The results are supported by experiments.
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    Editorial announcement (1999)
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    Circuits, systems and signal processing 18 (1999), S. i 
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    Topics: Electrical Engineering, Measurement and Control Technology
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    A concurrent system for the computation of higher-order moments (1999)
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    Circuits, systems and signal processing 18 (1999), S. 111-130 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The cumulants defined in terms of moments are basic to the study of higher-order statistics (HOS) of a stationary stochastic process. This paper presents a concurrent systolic array system for the computation of higher-order moments. The system allows for the simultaneous computation of the second-, third-, and fourth-order moments. The architecture achieves good speedup through its excellent exploitation of parallelism, pipelining, and reusability of some intermediate results. The computational complexity and system performance issues related to the architecture are discussed. The concurrent system is designed with the CMOS VLSI technology and is capable of operating at 3.9 MHz.
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    The invertibility of operators and contraction mappings (1999)
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    Circuits, systems and signal processing 18 (1999), S. 183-187 
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    Notes: Abstract Necessary and sufficient conditions for the invertibility of a (not necessarily linear) operatorN between normed linear spaces are given. It is shown thatN is invertible precisely if a certain operator associated withN is a contraction.
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    Circuit duality for recurrent Markov processes (1995)
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    Circuits, systems and signal processing 14 (1995), S. 187-211 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper investigates circuit Markov processes under the standpoint of duality principle.
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    Estimation of direction-of-arrivals based on the array manifold space (1995)
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    Circuits, systems and signal processing 14 (1995), S. 237-254 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper, a high resolution technique for estimating DOAs of spatially close source signals is presented. It is observed that the array manifold over a sector of interest is rank deficient and the dimension of the array manifold space, which is the range space of the array manifold, is less than the number of sensors in the array. The true signal subspace is a subspace in the array manifold space. A novel technique is provided that searches for the signal subspace in this array manifold space. The resulting estimated signal subspace has minimum principal angles with the data signal subspace generated by eigen-decomposing the covariance matrix of the array data vector. It is proved that the proposed estimator is asymptotically consistent and the estimated signal subspace is closer to the true signal subspace than the data signal subspace formed by MUSIC. The proposed novel technique has better performance than the MUSIC algorithm. Its performance is comparable to MLE and MD-MUSIC yet it requires only one-dimensional searches and is computationally much less intense. Simulation results are presented to show the effectiveness of the proposed technique, and comparisons with MUSIC, MLE, and MD-MUSIC algorithms are also included.
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    High-level synthesis: current status and future prospects (1995)
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    Circuits, systems and signal processing 14 (1995), S. 351-400 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract High-level synthesis is becoming increasingly important in the area of VLSI CAD. During the last decade, much research has been carried out in this area and some results have been achieved. This paper presents a survey on the state-of-the-art of current high-level synthesis research and applications. Besides basic knowledge, a comprehensive overview has been conducted among the various theories, methods, algorithms, and applications of the existing systems. Their advantages, limitations, and feasibilities are also described. Finally, some points on current status and future directions of high-level synthesis are addressed.
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    The running time-frequency distributions (1995)
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    Circuits, systems and signal processing 14 (1995), S. 401-414 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper introduces the running kernels that yield recursive structures for time-frequency distributions (TFDs). The running kernels offer important properties not possessed by the commonly used block distribution kernels. The introduced kernels allow an invariance in computations with respect to the extent of the kernel in the time or the lag variable. However, contrary to the wide class of block kernels that satisfy the desired timefrequency (t-f) properties, most recursive (running) time-frequency distributions (RTFDs) violate the marginal and the support properties. This paper considers both the direct and the indirect types of recursion and presents examples for illustration.
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    Robust estimation and signal detection with dependent nonstationary data (1995)
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    Circuits, systems and signal processing 14 (1995), S. 465-472 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper the dual topics of robust signal detection and robust estimation of a random variable are considered, where the data may be both dependent and nonstationary. We note that classical saddlepoint techniques for robustness do not readily apply in the dependent and/or nonstationary situation, and thus our results have application in a larger domain than what was feasible heretofore. In addition, our methods make possible the quantitative measurement of robustness and admit essentially arbitrary perturbations in an underlying joint statistical distribution away from the nominal. In particular, our methods show that the presence of dependency can result in a reduction of the robustness of the linear detector by approximately 50% and that appropriate censoring can improve this situation. We also show that, somewhat surprisingly, a weak amount of censoring can actually reduce robustness rather than increase it, even with dependent data that is “almost” independent. This calls into question the common practice, inspired by classical saddlepoint results for independent data, of employing censoring in cases where residual dependency is conceded. When applied to estimation, our work shows that for nominally Gaussian data, the conditional expectation estimator is optimal not only in terms of performance but also robustness (under appropriate performance measures), thus reinforcing the appeal of this estimator. On the other hand, for other performance measures, we also note that the conditional expectation estimator can be completely unrobust, regardless of whether the data is nominally Gaussian or not. Finally, our results establish a bound on estimator robustness.
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    Fast algorithms for selection of test nodes of an analog circuit using a generalized fault dictionary approach (1995)
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    Circuits, systems and signal processing 14 (1995), S. 707-724 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Selection of test nodes is an important phase of the fault dictionary approach. It is demonstrated in this paper that the techniques used for this purpose in other approaches of analog fault diagnosis like fault analysis and fault verification are not in general suitable for the fault dictionary approach. The ambiguity set is a simple and effective concept for choosing test nodes in the context of dictionaries. These sets are formed such that each faulty condition lies in only one ambiguity set. Deviating from this thinking, overlapping ambiguity sets are proposed in this paper, giving rise to a generalized fault dictionary. These sets use information more fully and hence reduce the number of test nodes. The concept of hashing is applied in this paper for selecting test nodes. This gives a linear time algorithm (linear in the number of fault voltage specificationsf′) and it isf′ times faster than the existing methods. It is not possible to select test nodes faster than this. This technique can also be used to select test nodes by the process of elimination of nodes. This is also linear inf′ per node elimination. Even a group of nodes can be eliminated or selected within the same computation. This freedom is not possible with the existing methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01204680
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    Nonlinear AR modeling (1995)
    Springer
    Circuits, systems and signal processing 14 (1995), S. 689-705 
    Details
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A major reason for the success of linear autoregressive (AR) modeling is that Kolmogrorov proved that every linear system could be represented by a linear AR model of infinite order. The computation of a finite order AR approximation is, of course, the practical goal. In this paper, we prove that every nonlinear system with a Volterra series expansion can be represented as a nonlinear AR model of infinite order. Our method shows how an approximation to any desired order and degree can be achieved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01213965
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  • 197
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    Beyond the Domain of Direct Observation: How to Specify a Probability Distribution that Represents the “State of Knowledge” About Uncertain Inputs (1999)
    Springer
    Risk analysis 19 (1999), S. 131-134 
    Details
    ISSN: 1539-6924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006914628988
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  • 198
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    Who Lives Near Coke Plants and Oil Refineries? An Exploration of the Environmental Inequity Hypothesis (1999)
    Springer
    Risk analysis 19 (1999), S. 171-186 
    Details
    ISSN: 1539-6924
    Keywords: Environment ; equity ; coke ; oil ; history ; risk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Facility-specific information on pollution was obtained for 36 coke plants and 46 oil refineries in the United States and matched with information on populations surrounding these 82 facilities. These data were analyzed to determine whether environmental inequities were present, whether they were more economic or racial in nature, and whether the racial composition of nearby communities has changed significantly since plants began operations. The Census tracts near coke plants have a disproportionate share of poor and nonwhite residents. Multivariate analyses suggest that existing inequities are primarily economic in nature. The findings for oil refineries are not strongly supportive of the environmental inequity hypothesis. Rank ordering of facilities by race, poverty, and pollution produces limited (although not consistent) evidence that the more risky facilities tend to be operating in communities with above-median proportions of nonwhite residents (near coke plants) and Hispanic residents (near oil refineries). Over time, the racial makeup of many communities near facilities has changed significantly, particularly in the case of coke plants sited in the early 1900s. Further risk-oriented studies of multiple manufacturing facilities in various industrial sectors of the economy are recommended.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006965325489
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    Fundamentals of Health Risk Assessment. Use, Derivation, Validity and Limitations of Safety Indices (1999)
    Springer
    Risk analysis 19 (1999), S. 231-247 
    Details
    ISSN: 1539-6924
    Keywords: Health risk assessment ; hazard characterization ; Acceptable Daily Intake ; Reference Dose ; paradigm ; practices ; cancer ; non-cancer ; Bayesian ; default options
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract We investigated the way results of human health risk assessments are used, and the theory used to describe those methods, sometimes called the “NAS paradigm.” Contrary to a key tenet of that theory, current methods have strictly limited utility. The characterizations now considered standard, Safety Indices such as “Acceptable Daily Intake,” “Reference Dose,” and so on, usefully inform only decisions that require a choice between two policy alternatives (e.g., approve a food additive or not), decided solely on the basis of a finding of safety. Risk is characterized as the quotient of one of these Safety Indices divided by an estimate of exposure: a quotient greater than one implies that the situation may be considered safe. Such decisions are very widespread, both in the U. S. federal government and elsewhere. No current method is universal; different policies lead to different practices, for example, in California's “Proposition 65,” where statutory provisions specify some practices. Further, an important kind of human health risk assessment is not recognized by this theory: this kind characterizes risk as likelihood of harm, given estimates of exposure consequent to various decision choices. Likelihood estimates are necessary whenever decision makers have many possible decision choices and must weigh more than two societal values, such as in EPA's implementation of “conventional air pollutants.” These estimates can not be derived using current methods; different methods are needed. Our analysis suggests changes needed in both the theory and practice of human health risk assessment, and how what is done is depicted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006973627307
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    Reliability Analysis for Hazardous Waste Treatment Processes (1999)
    Springer
    Risk analysis 19 (1999), S. 249-259 
    Details
    ISSN: 1539-6924
    Keywords: Reliability ; Monte Carlo simulation ; hazardous waste treatment ; safety factor ; packed tower ; activated sludge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The reliability of a treatment process is addressed in terms of achieving a regulatory effluent concentration standard and the design safety factors associated with the treatment process. This methodology was then applied to two aqueous hazardous waste treatment processes: packed tower aeration and activated sludge (aerobic) biological treatment. The designs achieving 95 percent reliability were compared with those designs based on conventional practice to determine their patterns of conservatism. Scoping-level treatment costs were also related to reliability levels for these treatment processes. The results indicate that the reliability levels for the physical/chemical treatment process (packed tower aeration) based on the deterministic safety factors range from 80 percent to over 99 percent, whereas those for the biological treatment process range from near 0 percent to over 99 percent, depending on the compound evaluated. Increases in reliability per unit increase in treatment costs are most pronounced at lower reliability levels (less than about 80 percent) than at the higher reliability levels (greater than 90 percent, indicating a point of diminishing returns. Additional research focused on process parameters that presently contain large uncertainties may reduce those uncertainties, with attending increases in the reliability levels of the treatment processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006925711377
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