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At least 19 recordsLinked to original sources
PubMed2002

A blueprint for the problem formulation phase of EPA-type ecological risk assessments for 316(b) determinations.

The difference between management objectives focused on sustainability of fish populations and the indigenous aquatic community, and a management objective focused on minimizing entrainment and impingement losses accounts for much of the ongoing controversy surrounding paragraph 316(b). We describe the EPA's ecological risk assessment framework and recommend that this framework be used to more effectively address differences in management objectives and structure paragraph 316(b) determinations. We provide a blueprint for the problem formulation phase of EPA-type ecological risk assessments for cooling-water intake structures (CWIS) at existing power plant facilities. Our management objectives, assessment endpoints, conceptual model, and generic analysis plan apply to all existing facilities. However, adapting the problem formulation process for a specific facility requires consideration of the permitting agency's guidelines and level of regulatory concern, as well as site-specific ecological and technical differences. The facility-specific problem formulation phase is designed around the hierarchy of biological levels of organization in the generic conceptual model and the sequence of cause-effect events and risk hypotheses represented by this model. Problem formulation is designed to be flexible in that it can be tailored for facilities where paragraph 316(b) regulatory concern is low or high. For some facilities, we anticipate that the assessment can be completed based on consideration of susceptibility alone. At the other extreme, a high level of regulatory concern combined with the availability of extensive information and consideration of costly CWIS mitigation options may result in the ecological risk assessment relying on analyses at all levels. Decisions on whether to extend the ecological risk assessment to additional levels should be based on whether regulatory or generator concerns merit additional analyses and whether available information is adequate to support such analyses. In making these decisions, the functional dependence between levels of analysis must be considered in making the transition to the analysis phase and risk estimation component of the ecological risk assessment. Regardless of how the generic analysis plan is modified to develop a facility-specific analysis plan, the resulting plan should be viewed as a tool for comparing representative species and alternative CWIS options by focusing on relative changes (i.e., proportional or percent changes) in various measures. The analysis plan is specifically designed to encourage consideration of multiple lines of evidence and to characterize uncertainties in each line of evidence. Multiple lines of evidence from different levels of analysis, obtained using both prospective and retrospective techniques, provide a broader perspective on the magnitude of potential effects and associated uncertainties and risks. The implications of the EPA's recent (April 2002) proposed regulations for existing facilities on the applicability of this blueprint are briefly considered.

Animals↗
PubMed2004

Ecological risk assessment and problem formulation for Lake Uluabat, a Ramsar State in Turkey.

Unlike the United States and the European Union, developing countries do not have sufficiently structured legal and institutional systems to apply certain environmental management tools such as ecological risk assessment. However, it is important for countries with valuable environmental and ecological resources to have appropriate tools and to strengthen their environmental management capabilities and capacities for the sake of those resources. The case study described in this paper attempts to be a case study towards developing environmental management plans, especially in developing countries. The problem formulation step of Ecological Risk Assessment applied in this study contributed to the basic elements of an environmental management plan including the following: the partnership-building process, prioritization of the problems and issues of the ecosystem, and development of the action plan. Based on the information provided by participants from a series of workshops held to develop an environmental management plan for Uluabat Lake, ecosystem risks were ranked and an action plan was formed. The results obtained with the aid of fuzzy set theory provided a base for identification of the action steps by allowing scientific information to be included in the process. The degree to which Uluabat Lake's problem formulation fits into the existing legal framework of Turkey is also analyzed in this paper.

Conservation of Natural Resources↗
PubMedDate not supplied

Community-based research--a framework for problem formulation: the case of upper endoscopy for gastroesophageal reflux disease.

OBJECTIVE: To identify clinical hypotheses and information gaps underlying disagreement about the use of upper gastrointestinal endoscopy (EGD) for the diagnosis of gastroesophageal reflux disease (GERD), and to design a registry study to test these hypotheses. DESIGN AND SETTING: Structured group discussions with community-based practicing gastroenterologists. RESULTS: Thirty-three gastroenterologists from 17 sites discussed a set of clinical scenarios concerning the use of EGD in GERD patients with different clinical histories. Clinicians identified patient characteristics and outcome variables missing from the original problem formulation. Using decision tables, the combinations of patient characteristics that provoked disagreement among clinicians were determined. The resulting decision tables specified which characteristics and outcome variables should be measured to test competing clinical theories of when to use EGD in patients with GERD. Subsequently, the clinicians conducted a practice-based study measuring uncertain variables associated with disagreement about the need for EGD in specific clinical situations. CONCLUSION: A structured, but flexible, approach to group discussion may help identify factors that are important in decision making and the hypotheses that should be addressed in resolving variations in practice styles. Technology assessors can use these methods to identify variables underlying clinicians' concerns about the clinical validity of recommendations about practice. This experience with eliciting patient characteristics and uncertain variables underscores the importance of involving practicing clinicians in the process and could be a useful model for problem formulation in guideline development and in community-based research.

Adult↗
PubMed1999

Modeling methods for mixture-of-mixtures experiments applied to a tablet formulation problem.

During the past few years, statistical methods for the experimental design, modeling, and optimization of mixture experiments have been widely applied to drug formulation problems. Different methods are required for mixture-of-mixtures (MoM) experiments in which a formulation is a mixture of two or more "major" components, each of which is a mixture of one or more "minor" components. Two types of MoM experiments are briefly described. A tablet formulation optimization example from a 1997 article in this journal is used to illustrate one type of MoM experiment and corresponding empirical modeling methods. Literature references that discuss other methods for MoM experiments are also provided.

Algorithms↗
PubMed2004

A benchmark for methods in reverse engineering and model discrimination: problem formulation and solutions.

A benchmark problem is described for the reconstruction and analysis of biochemical networks given sampled experimental data. The growth of the organisms is described in a bioreactor in which one substrate is fed into the reactor with a given feed rate and feed concentration. Measurements for some intracellular components are provided representing a small biochemical network. Problems of reverse engineering, parameter estimation, and identifiability are addressed. The contribution mainly focuses on the problem of model discrimination. If two or more model variants describe the available experimental data, a new experiment must be designed to discriminate between the hypothetical models. For the problem presented, the feed rate and feed concentration of a bioreactor system are available as control inputs. To verify calculated input profiles an interactive Web site (http://www.sysbio.de/projects/benchmark/) is provided. Several solutions based on linear and nonlinear models are discussed.

Algorithms↗
PubMed2006

Megavariate analysis of environmental QSAR data. Part II--investigating very complex problem formulations using hierarchical, non-linear and batch-wise extensions of PCA and PLS.

Three extensions of the basic PCA and PLS methodologies are described. These extensions are hierarchical, non-linear and batch-based in nature. The objectives of these methods are to assist in problem understanding and problem solving in very complex (QSAR) problem formulations. The method extensions are illustrated using two example QSAR data sets containing many X- and Y-variables.

Hazardous Substances↗
PubMed2005

MEG forward problem formulation using equivalent surface current densities.

We present a formulation for the magnetoencephalography (MEG) forward problem with a layered head model. Traditionally the magnetic field is computed based on the electric potential on the interfaces between the layers. We propose to express the effect of the volumetric currents in terms of an equivalent surface current density on each interface, and obtain the magnetic field based on them. The boundary elements method is used to compute the equivalent current density and the magnetic field for a realistic head geometry. We present numerical results showing that the MEG forward problem is solved correctly with this formulation, and compare it with the performance of the traditional formulation. We conclude that the traditional formulation generally performs better, but still the new formulation is useful in certain situations.

Animals↗
PubMed1995

Use of knowledge bases and QSARs to estimate the relative ecological risk of agrichemicals: a problem formulation exercise.

Ecological risk assessments can be used to establish the likelihood that an adverse effect will result from exposure to one or more chemicals. When evaluating contaminated sites with many chemicals present, risk assessors must grapple with the problem of quickly identifying the chemicals that are most likely to be of concern, based on effect and exposure assessment information. Many times data gaps exist and the risk assessor is left with decisions on which models to use to estimate the parameter of concern. In the present paper, a procedure is presented for ranking agrichemicals, utilizing the ASTER (ASsessment Tools for the Evaluation of Risk) system. The procedure was employed to rank the relative ecological risk of forty-nine pesticides historically used in agricultural sites in the Walnut Creek watershed near Ames, lowa, USA. Empirical data from the ASTER system were used when available in the associated databases, and quantitative structure-activity relationships and expert systems were invoked when data were lacking. Separate rankings were conducted based on major species taxonomic groupings. Resulting toxic effects thresholds were compared to surface water concentrations.

Agrochemicals↗
PubMed1985

Transesterification: an analytical and formulation problem.

A range of esters including salicylates, nicotinates and parabens have been shown to undergo reversible, base-catalysed transesterification in hydroalcoholic solutions. In non-alcoholic solution phenyl salicylate undergoes a concentration-dependent oligomerization which yields salsalate and other products. The transesterification reactions also occur in products formulated for topical use, which have vehicles based upon alcohol, glycol or glycol polymers. Without recognition, such reactions may compromise stability assessments, pharmaceutical integrity and delivery profiles.

Journal Article↗