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PubMed2001

Using conceptual models of nursing to guide nursing research: the case of the Neuman systems model.

Conceptual models of nursing inform thinking and give meaning and direction to nursing research. The Neuman systems model is used to exemplify the following five steps, which provide specific direction for conceptual model-based research: (a) Develop a comprehensive understanding of the substantive content and research rules of the conceptual model, (b) review existing research guided by the conceptual model, (c) construct a conceptual-theoretical-empirical structure, (d) clearly communicate the conceptual-theoretical-empirical structure, and (e) conclude the report with an evaluation of the empirical adequacy of the middle-range theory and the credibility of the conceptual model.

Humans↗

PubMed1998

Empirical verification of a theoretical model derived from the Roy adaptation model: findings from five studies.

This article presents a theoretical model derived from the Roy adaptation model and the findings of an empirical verification of this model from five studies. Four groups of subjects were included in the studies: informal caregivers of demented relatives at home, informal caregivers of psychiatrically ill relatives at home, professional caregivers of elderly institutionalized patients, and aged spouses in the community. In at least three studies, a number of theoretical propositions derived from the Roy adaptation model were supported using LISREL VIII, thus adding credence to some tenets of Roy's model. Particularly, the focal stimulus of perceived stress, the contextual stimulus of conflicts in the exchange of social support, and one component of the coping mechanisms (the passive/avoidance coping strategies) were positively linked directly or indirectly with psychological distress, which is an indicator of adaptation in the self-concept mode. Given their importance, these elements should be considered in the development of a middle-range theory of psychological adaptation derived from the Roy adaptation model.

Adaptation, Psychological↗

PubMed1998

Empirical testing of a longitudinal model derived from the Roy adaptation model.

This article presents the steps and results of the empirical testing of a theoretical longitudinal model, derived from Roy's nursing conceptual model, of the psychosocial determinants of adaptation in different target groups. The model was elaborated and empirically verified based on the integrated results of four longitudinal studies involving groups vulnerable to mental health problems. By means of structural equation analyses, the cross-sectional model was verified at two points in time. The results showed that the model was relatively stable over time. The model was also tested using longitudinal data. Results showed little consistency in the patterns of relationships across studies. The significant links that emerged from the analyses shed some light on the complexity of the process of adaptation to different types of stressors. They underscore the importance for nursing practice to develop interventions aimed at certain variables: perceived stress, conflicts in the exchange of support, and passive and avoidance coping strategies. The results also highlight the importance of the relationship between perceived stress, passive/avoidance coping strategies and psychological distress.

Adaptation, Psychological↗

PubMed2003

Models of breast cancer: quo vadis, animal modeling?

Rodent models for breast cancer have for many decades provided unparalleled insights into cellular and molecular aspects of neoplastic transformation and tumorigenesis. Despite recent improvements in the fidelity of genetically engineered mice, rodent models are still being criticized by many colleagues for not being 'authentic' enough to the human disease. Motives for this criticism are manifold and range from a very general antipathy against the rodent model system to well-founded arguments that highlight physiological variations between species. Newly proposed differences in genetic pathways that cause cancer in humans and mice invigorated the ongoing discussion about the legitimacy of the murine system to model the human disease. The present commentary intends to stimulate a debate on this subject by providing the background about new developments in animal modeling, by disputing suggested limitations of genetically engineered mice, and by discussing improvements but also ambiguous expectations on the authenticity of xenograft models to faithfully mimic the human disease.

Animals↗

PubMed2006

Mathematical modeling of an aqueous film coating process in a Bohle Lab-Coater: part 2: application of the model.

For the prediction of the air and product temperatures, the product moisture, and the air humidity during a coating process in a Bohle Lab-Coater, a model was developed. The purpose of this work was to determine the limit moisture, the critical moisture, and the constant for the exchange rate between both zones and to use these values for other sets of experiments to test the model. The adaptation of the 3 parameters (limit moisture, critical moisture, and exchange rate constant) was done by calculation of the product temperature in both zones for several sets of parameters in order to minimize the sum of square deviation between the calculated and the measured product temperatures. This set of parameters was used to test the validity of the model. By applying the model, the product temperature could be predicted based on the product, process, and equipment-related parameters. Hence, the model can be used to theoretically investigate the influence of different process parameters. The mean difference between the predicted and measured product temperatures in the steady state is approximately 2 up to 3 K using the determined parameter set for the limit moisture, the critical moisture, and the exchange rate constant. The model is useful for the prediction of the air and product temperatures, the product moisture, and air humidity during a coating process in the Bohle Lab-Coater using round, biconvex tablets.

Chemistry, Pharmaceutical↗

PubMed2002

Animal in vivo models of EBV-associated lymphoproliferative diseases: special references to rabbit models.

Animal models of human EBV-associated diseases are essential to elucidate the pathogenesis of EBV-associated diseases. Here we review those previous models using EBV or EBV-like herpesviruses and describe the details on our two newly-developed rabbit models of lymphoproliferative diseases (LPD) induced by simian EBV-like viruses. The first is Cynomolgus-EBV-induced T-cell lymphomas in rabbits inoculated intravenously (77-90%) and orally (82-89%) during 2-5 months. EBV-DNA was detected in peripheral blood by PCR from 2 days after oral inoculation, while anti-EBV-VCA IgG was raised 3 weeks later. Rabbit lymphomas and their cell lines contained EBV-DNA and expressed EBV-encoded RNA-1 (EBER-1). Rabbit lymphoma cell lines, most of which have specific chromosomal abnormality, showed tumorigenicity in nude mice. The second is the first animal model for EBV-infected T-cell LPD with virus-associated hemophagocytic syndrome (VAHS), using rabbits infected with an EBV-like herpesvirus, Herpesvirus papio (HVP). Rabbits inoculated intravenously with HVP-producing cells showed increased anti-EBV-VCA-IgG titers, and most (85%) subsequently died of fatal LPD and VAHS, with bleeding and hepatosplenomegaly, during 22-105 days. Peroral spray of cell-free HVP induced viral infection with seroconversion in 3 out of 5 rabbits, with 2 of the 3 infected rabbits dying of LPD with VAHS. Atypical T lymphocytes containing HVP-DNA and expressing EBER-1 were observed in many organs. Hemophagocytic histiocytosis was observed in the lymph nodes, spleen, bone marrow, and thymus. These rabbit models are also useful and inexpensive alternative experimental model systems for studying the biology and pathogenesis of EBV, and prophylactic and therapeutic regimens.

Animals↗

PubMed2003

Issues of replicability in Monte Carlo modeling: a case study with a pesticide leaching model.

Sensitivity and uncertainty analyses based on Monte Carlo sampling were undertaken for various numbers of runs of the pesticide leaching model (PELMO). Analyses were repeated 10 times with different seed numbers. The ranking of PELMO input parameters according to their influence on predictions for leaching was stable for the most influential parameters. For less influential parameters, the sensitivity ranking was severely influenced by the seed number used. For uncertainty analyses, probabilities of exceeding a particular concentration were significantly influenced by the seed number used in the random sampling of values for the two parameters considered, even for those cases in which 5,000 model runs were undertaken (coefficient of variation of 10 replicated analyses, 5%). A decrease in the variability of exceedance probabilities could be achieved by further increasing the number of model runs. However, this may prove to be impractical when complex deterministic models with a relatively long running time are used. Attention should be paid to replicability aspects by modelers when devising their approach to assessing the uncertainty associated with the modeling and by decision makers when examining the results of probabilistic approaches.

Environmental Monitoring↗

PubMed2005

Quantitative identification of sources of dioxin-like polychlorinated biphenyls in sediments by a factor analysis model and a chemical mass balance model combined with Monte Carlo techniques.

The major sources of dioxin-like polychlorinated biphenyls (PCBs) in two sediment cores from Tokyo Bay and Lake Shinji (both in Japan) were identified and their source contributions estimated using two receptor models. The first was a nonnegative constrained factor analysis (FA) model, and the second was a nonnegative constrained chemical mass balance model combined with Monte Carlo techniques (CMB-MC) to take into account the variability and uncertainty in both PCB congener profiles of sources and environmental samples. According to the FA model, variations in the concentrations of dioxin-like PCBs in each sediment core were accounted for almost entirely by two factors, which were considered to correspond to Kanechlors (KCs; Japanese PCB products) and incineration. The CMB-MC model investigated the trends of the burdens from four types of KCs and incineration to the concentrations of dioxin-like PCBs in each sediment core. The results for both sediment cores obtained by both models indicated that the burden from KCs increased gradually beginning in the 1950s, peaked around 1970, and declined thereafter, whereas the burden from incineration increased gradually from the 1950s to the early 1990s. The estimated contribution from incineration to the toxic equivalent concentration of dioxin-like PCBs was comparable to that from KCs.

Dioxins↗

PubMed2006

Agent-based modeling of drinking behavior: a preliminary model and potential applications to theory and practice.

OBJECTIVES: We developed a preliminary agent-based simulation model designed to examine agent-environment interactions that support the development and maintenance of drinking behavior at the population level. METHODS: The model was defined on a 1-dimensional lattice along which agents might move left or right in single steps at each iteration. Agents could exchange information about their drinking with each other. In the second generation of the model, a "bar" was added to the lattice to attract drinkers. RESULTS: The model showed that changes in drinking status propagated through the agent population as a function of probabilities of conversion, rates of contact, and contact time. There was a critical speed of population mixing beyond which the conversion rate of susceptible nondrinkers was saturated, and the bar both enhanced and buffered the rate of propagation, changing the model dynamics. CONCLUSIONS: The models demonstrate that the basic dynamics underlying social influences on drinking behavior are shaped by contacts between drinkers and focused by characteristics of drinking environments.

Alcohol Drinking↗

PubMed1992

Measurement, analysis, and modelling of the caloric response. 1. A descriptive mathematical model of the caloric response over time.

A mathematical model for describing the caloric response over time offers many important advantages over the commercially-available qualitatively-fitted curves that are now used by the clinician for evaluating caloric results. In this report advances in the development of a nonlinear least-squares mathematical model are discussed and the roles and derivations of fitting parameters and curve-derived indices are outlined. This model provides a rigorous and objective description of the caloric response in its entirety with four continuous parameters. These fitting parameters make it possible to 1) describe individual caloric responses precisely and uniquely, 2) compare pairs of individual caloric responses or groups of caloric responses statistically, 3) extract information not previously available, 4) quantify variability within the caloric response, and 5) model physical properties of the caloric stimulus and physiological variables affecting the caloric response. Results from this model are compared with the results from our earlier models and with traditional multiparameter caloric results.

Caloric Tests↗

PubMed1975

Rumen modeling: rumen input-output balance models.

Two models of rumen fermentative relationships expressed as systems of simultaneous linear equations and based on requirements for maintenance of balances of elementary imput and output and metabolic pathways are presented in matrix format consistent with solution by linear programs. Matrix entries defining the two models were verified carefully based upon a survey of the literature, and conceptual bases of the models were validated by comparisons of model outputs with experimental data not used in model construction. The models then were used to evaluate interactions among feed composition, volatile fatty acid yields and patterns, microbial growth yields and efficiencies, and microbial metabolic pathways.

Amino Acids↗

PubMed1999

Influences of the Unified Service Action Model on the HL7 Reference Information Model.

Modeling information for the electronic medical record (EMR) builds on a century of study on information and its relationship to cost and quality improvement. An initiative to examine the focus of cost and quality improvement and its relationship to information modeling resulted in the development of the Unified Service Action Model of healthcare processes, which focuses on the action as the center of cost accounting, quality accounting and privacy management. The application of this model to the HL7 Reference Information Model produced a simplification of the HL7 model at the cost of increased reliance on vocabulary terms for actions.

Costs and Cost Analysis↗

PubMedDate not supplied

[The interactive determination of the mathematical model parameters for the planning of the radiation therapy of malignant tumors. 2. A method of adjusting the mathematical model parameters for calculating the tolerance doses and probabilities of the occurrence of radiation complications in body organs and tissues].

To enhance the accuracy of calculation of tolerance doses, adequate doses and the likelihood of radiation complications in normal organs and tissues, a method has been developed for local model parameter adjustment (LMPA) by using mathematical models. It includes the analysis of the structure of a mathematical model, the systematization of clinical data and their goal-oriented use for model adjustment. The necessity of developing a new research line (LMPA) is determined by the complexity of the irradiated organism as a system and by the attempts to take into account the impact of the system on the parameters of mathematical models. LMPA can be considered to generalize determination of the parameters of mathematical models or their directed (interactive) determination. The strategy of using LMPA, which is based on the preset radiation treatment protocol and its respective dosage distributions in normal organs and tissues, is described. The efficiency of LMPA is shown to depend on the volume and relevance of clinical data that the radiological therapist has at his disposal.

Computer Simulation↗

PubMed2001

A dermal model for spray painters. Part I: subjective exposure modelling of spray paint deposition.

The discriminative power of existing dermal exposure models is limited. Most models only allow occupational hygienists to rank workers between and within workplaces according to broad bands of dermal exposure. No allowance is made for the work practices of different individuals. In this study a process-based, structured approach has been used to estimate dermal exposure from overspray generated by a spray painting process. Factors for spray technique, object shape and workers' individual work practices involved in the processes of droplet formation and deposition were incorporated into the model. The model was applied to predict dermal exposure of airless spray painters and the results were compared with exposure data. The predicted levels of exposure showed reasonable rank correlation with the measured exposure, although the model tended to over-predict the actual level of exposure. It was concluded that a structured, process-based approach has the potential to produce reliable estimates of dermal exposure. The reliability of exposure models of this type should be explored further and the relationship between the determinants of exposure should be validated by additional field studies.

Air Pollutants, Occupational↗

PubMed2001

[Modeling of feeling institution in pilot structural model].

Objective. To improve a structural pilot model proposed by R. A. Hess, in which element of observation feeling institution was neglected. Method. Real simulation results showed that there was a blind region for small observation signal, and pilot made no response in this region. So we knew that the basic characteristics of the observation feeling institution were observation threshold and observation noise. A Neural Network (NN) receptor model was augmented in the structural pilot model to describe the characteristics of human observation feeling institution. Furthermore, using the augmented model, the affection of the pilot model on the characteristics of the closed-loop system of pilot and controlled element was studied. Result. The affection of NN perception on the closed-loop system was that the stable gain region of the human pilot was extended. Conclusion. The proposed model was reasonable for the element of human feeling institution.

Aerospace Medicine↗

PubMed2003

Bayesian approach for the calibration of models: application to an urban stormwater pollution model.

In environmental modelling, estimating the confidence level in conceptual model parameters is necessary but difficult. Having a realistic estimation of the uncertainties related to the parameters is necessary i) to assess the possible origin of the calibration difficulties (correlation between model parameters for instance), and ii) to evaluate the prediction confidence limits of the calibrated model. In this paper, an application of the Metropolis algorithm, a general Monte Carlo Markov chain sampling method, for the calibration of a four-parameter lumped urban stormwater quality model is presented. Unlike traditional optimisation approaches, the Metropolis algorithm identifies not only a "best parameter set", but a probability distribution of parameters according to measured data. The studied model includes classical formulations for the pollutant accumulation during dry weather period and their washoff during a rainfall event. Results indicate mathematical shortcomings in the pollutant accumulation formulation used.

Algorithms↗

PubMed2004

Comparison of proportional hazard model and neural network models in a real data set of intensive care unit patients.

There has been increased interest in using neural network model (NNM) for prognosis tasks. However, the performance of NNM has seldom been compared with that of traditional statistical models such as proportional hazard model (PHM) in real data sets. We conducted a comparative study of PHM and two types of NNM, that is, aggregate single point model (ASPM) and multiple point model (MPM), using a real data set of intensive care unit patients. The three models were developed using the 70% training subset and their predictive accuracy were assessed using the 30% testing subset according to classification accuracy, area under receiver operating curve, and concordance index. Overall, the highest predictive accuracy was found in MPM, followed by PHM and ASPM. MPM is likely to have the potential ability to provide more accurate estimation of prognosis than PHM and ASPM

Area Under Curve↗

PubMed2005

Developing an independent, generic, phosphorus modelling component for use with grid-oriented, physically based distributed catchment models.

Grid-oriented, physically based catchment models calculate fields of various hydrological variables relevant to phosphorus detachment and transport. These include (i) for surface transport: overland flow depth and flow in the coordinate directions, sediment load, and sediment concentration and (ii) for subsurface transport: soil moisture and hydraulic head at various depths in the soil. These variables can be considered as decoupled from any chemical phosphorus model since phosphorus concentrations, either as dissolved or particulate, do not influence the model calculations of the hydrological fields. Thus the phosphorus concentration calculations can be carried out independently from and after the hydrological calculations. This makes it possible to produce a separate phosphorus modelling component which takes as input the hydrological fields produced by the catchment model and which calculates, at each simulation time step, the phosphorus concentrations in the flows. This paper summarises the equations and structure of such a Grid Oriented Phosphorus Component (GOPC) developed by the authors for simulating phosphorus concentrations and loads using the outputs of a fully distributed physical based hydrological model. The GOPC performance is illustrated by an example of a simplified hypothetical catchment subjected to some ideal conditions.

Fertilizers↗