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At least 991 records · Page 55Linked to original sources
PubMed1996

Risk assessment in the regulatory process for wetlands.

This paper presents an ecosystem-based approach to risk assessment in freshwater wetlands. The key concept in this approach is that the primary biotic and abiotic components that determine the structural and functional characteristics of wetlands are inseparable. Each component should be identified and its contribution to ecosystem functions or human values determined when deciding whether a stressor poses an unreasonable risk to the sustainability of a particular wetland. Understanding the major external and internal factors that regulate the operational conditions of wetlands is critical to risk characterization. Determining the linkages between these factors, and how they influence the way stressors affect wetlands, is the basis for an ecosystem approach. Adequate consideration of wetland ecology, hydrology, geomorphology, and soils can greatly reduce the level of uncertainty associated with risk assessment and lead to more effective risk management. In order to formulate effective solutions, wetland problems must be considered at watershed, landscape, and ecosystem scales.

Animals↗
PubMed1997

Application of genetic algorithms to parameter estimation of bioprocesses.

The paper explains the application of a genetic algorithm (GA) to the problem of estimating parameters for a kinetic model of a biologically reacting system. It is demonstrated that the GA is a powerful tool for quantifying the kinetic parameters using kinetic data. As the operation of the GA does not depend on the form of the model equation, it can be applied to the wide spectrum of kinetic modelling problems without any complex formulation procedure.

Algorithms↗
PubMed2006

Mum, why do you keep on growing? Impacts of environmental variability on optimal growth and reproduction allocation strategies of annual plants.

In their 1990 paper Optimal reproductive efforts and the timing of reproduction of annual plants in randomly varying environments, Amir and Cohen considered stochastic environments consisting of i.i.d. sequences in an optimal allocation discrete-time model. We suppose here that the sequence of environmental factors is more generally described by a Markov chain. Moreover, we discuss the connection between the time interval of the discrete-time dynamic model and the ability of the plant to rebuild completely its vegetative body (from reserves). We formulate a stochastic optimization problem covering the so-called linear and logarithmic fitness (corresponding to variation within and between years), which yields optimal strategies. For "linear maximizers'', we analyse how optimal strategies depend upon the environmental variability type: constant, random stationary, random i.i.d., random monotonous. We provide general patterns in terms of targets and thresholds, including both determinate and indeterminate growth. We also provide a partial result on the comparison between ;"linear maximizers'' and "log maximizers''. Numerical simulations are provided, allowing to give a hint at the effect of different mathematical assumptions.

Algorithms↗
PubMed1996

A mathematical model for drug administration by using the phagocytosis of red blood cells.

A mathematical model for the delivery of drug directly to the macrophages by using the phagocytosis of senescent red blood cells is proposed. The model is based on the following assumption: At time t = 0 a preassigned red blood cell population n(0,a) = phi (a), a > 0, loaded by the drug, is injected in the blood circulation. Among the cells of that population only those with an age a > or = a (a = 120 days) will be phagocytosed by macrophages. Of course, the lifetime of the drug must be higher than a. Within the red blood cells it cannot be metabolized, neither can it diffuse through their membranes. The emphasis of the paper is on the mathematical properties and on the formulation of the control problem.

Drug Therapy↗
PubMed2006

A new organ transplantation location-allocation policy: a case study of Italy.

In this paper, we propose a location model for the optimal organization of transplant system. Instead of simulation approach, which is typical when facing many health care applications, our approach is distinctively based on a mathematical programming formulation of the relevant problem. In particular, we focus on the critical role of time in transplantation process as well as on a spatial distribution of transplant centers. The allocation of transplantable organs across regions with the objective of attaining regional equity in health care, is the aim of this paper. Our model differs from previous modeling approaches in that it considers the nationwide reorganization of the transplant system, identifying system barriers that may impair equity and efficiency. The demolition of these barriers may leads on a reduction of waiting lists and of wasted organs. We provide the basic structure and the properties of the model, and validate it on a real case study. The experimental validation of the model demonstrates the effectiveness and robustness of our proposal.

Efficiency, Organizational↗
PubMed1984

Mathematical principles of cell division.

The report given here is an attempt of the mathematical formulations to solve a problem concerning cell division and the control of mass and volume of the nucleus and cytoplasm. The study of the interaction forces on the nucleus and the vibrational frequencies during cell division are analyzed in detail. Lastly, the vibrations of a cell and the coalescence of the vacuoles inside a living plant cell are discussed theoretically.

Animals↗
PubMed1985

Constitutive stress--strain relations for the myocardium in diastole.

The importance of stress-strain myocardial constitutive relations is that they provide a criterion for behavior in vivo. Our purpose was to develop constitutive equations which are valid in diastole. The myocardium was assumed to be composed of a nonlinear viscoelastic, inhomogeneous, anisotropic (transversely isotropic) and incompressible material operating under adiabatic and isothermal conditions. The expressions contain five moduli. Two are fixed by the restriction of incompressibility, one is estimated, the remaining two refer to directions along and perpendicular to a fiber. Both possess a bimodal variation with intermodal switching occurring in late rapid filling and diastasis. They are functions of time and material constants. These constants can be observed. A dynamic test is suggested. Constitutive statements complete a set of equations sufficient for the solution of a class of boundary value problems. One type is formulated. They also permit the determination of stress from measured strain. Examples are given.

Heart↗
PubMed1995

A Bayesian framework for understanding texture segmentation in the primary visual cortex.

This paper presents a mathematical theory for understanding the computations involved in texture segmentation in the primary visual cortex. We propose that texture segmentation is a part of the early visual system's overall strategy to infer surfaces of objects in a visual scene. Based on this insight, we use the Bayesian inference paradigm to formulate the texture segmentation problem into a maximum a posteriori surface inference problem. The dynamical system for finding the optimal solution of this problem can be characterized by two concurrent and interactive processes: a gradual sharpening of the boundary signals and a simultaneous smoothing of the surface signals. The behavior of these dynamical processes was studied using both analytical and computational methods. We present some computational results and mathematical predictions. This theory suggests a novel framework for understanding the functional roles of the complex cells in the primary visual cortex.

Bayes Theorem↗
PubMed1989

A systems approach to child abuse: management and treatment issues.

In the systems approach certain patterns of family interaction are seen as fitting with physical abuse towards children in the family. If these interactions are blocked or changed using specific family therapy interventions, the risk of further abuse will be significantly reduced. Identifying typical patterns of interaction that fit with abuse is a useful first step in planning the management of physically abusing families. A full systemic formulation of the presenting problem will address numerous systems and sub-systems simultaneously, notably the family-professional system, the family within the extended family/friendship system, and the nuclear family. Interventions may have to be directed on a variety of these levels. The Marlborough Family Service has assessed and treated over 100 child-abusing families. A family day unit is used as the setting, and a multifamily group as the principle medium of treatment. Within the day unit real life stress situations are recreated around everyday issues, enabling families to find new and nonviolent solutions to the problems of daily life. In the cases seen, approximately one-third have resulted in a recommendation of permanent alternative family care for the children. In those families reunited, the re-injury rate has been found to be extremely low.

Child↗
PubMed1986

A successful psychiatric training program for medical residents.

The psychosocial skills of 24 PGY I medical residents receiving psychiatric training every other week during the internship year were evaluated and compared to a control group of 13 PGY I residents. After the internship year, the psychiatrically trained residents showed an increase in their ability to recognize emotional problems, whereas the control group recognized less depression. Psychiatrically trained residents were more sophisticated in psychosocial problem descriptions and plan formulations, whereas the control group formulated more poor psychosocial plans.

Clinical Competence↗
PubMed1995

WENDEC: a deconvolution program for processing hormone time-series.

The estimation of the glandular secretory rate from time-series of hormone concentration in plasma can be formulated as a deconvolution problem. In particular, the paper addresses the analysis of frequently sampled data collected in order to study spontaneous pulsatile secretion. Standard deconvolution methods do not allow for the non-negativity constraint and the presence of high-frequency components in the secretory rate. In order to overcome the intrinsic ill-conditioning of the problem, the maximum entropy method is used to obtain a probabilistic representation of the prior knowledge concerning the unknown secretory signal, thus leading to a White Exponential Noise (WEN) model. The deconvolution problem is then posed within a Bayesian framework and solved by means of Maximum-A-Posteriori estimation. The program that implements the algorithm handles non-negativity constraints, provides confidence intervals, and is computationally and memory efficient.

Algorithms↗
PubMed1992

Theory and practice and the preparation of teachers of nursing.

Questions of the relationship between theory and practice frequently occur both within educational and nursing literature and they are the questions that are going to be explored in this paper. Like the double helix, this paper is going to intertwine and interlink nursing and education, since they possess so many similarities and the overall thesis of the paper is that the relationship between theory and practice presents problems because the nature of the problem has been inadequately formulated. The paper falls into four main parts: 1. Four types of relationship between theory and practice. 2. Nursing and education as fields of practice and the nature of fields of practice--implications of this for knowledge, skills, attitudes and values--skills/practical knowledge/knowledge how. 3. Nature of the fields of study and the implications of this for knowledge. 4. Theory and practice--eight possible relationships. The conclusion offers a tentative reformulation of theory and practice in terms of probability and relates this to the preparation of nurses and teachers.

Education, Nursing↗
PubMed1995

Optimization of rotational radiotherapy treatment planning.

PURPOSE: Rotational therapy treatment planning for rotationally symmetric geometry of tumor and healthy tissue provides an important example of testing various approaches to optimizing dose distributions for therapeutic x-ray irradiations. In this article, dose distribution optimization is formulated as a variational problem. This problem is solved analytically and numerically. METHODS AND MATERIALS: The classical Lagrange method is used to derive equations and inequalities that give necessary conditions for minimizing the mean-square deviation between the ideal dose distribution and the achievable dose distribution. The solution of the resulting integral equation with Cauchy kernel is used to derive analytical formulas for the minimizing irradiation intensity function. RESULTS: The solutions are evaluated numerically and the graphs of the minimizing intensity functions and the corresponding dose distributions are presented. CONCLUSIONS: The optimal solutions obtained using the mean-square criterion lead to significant underdosage in some areas of the tumor volume. Possible solutions to this shortcoming are investigated and medically more appropriate criteria for optimization are proposed for future investigations.

Humans↗
PubMed2004

Managing under managed community care: the experiences of clients, providers and managers in Ontario's competitive home care sector.

In 1996, a newly elected government in the Province of Ontario, Canada, introduced a managed competition environment into the home care sector through the establishment of a competitive contracting process for home care services. Through 65 in-depth, semi-structured interviews conducted between November 1999 and January 2001, we trace the implementation of this competitive contracting policy within Ontario's newly established managed community care environment and assess the effects of competitive contracting against two sets of goals: (1). quality of care goals that consider continuity of care of paramount importance in the provision of home care; and (2). the managed competition goal of increased efficiency. In assessing the implementation of this policy against these goals, we highlight the conflicts that can arise in pursuing different policy goals in response to different formulations of the policy problem that underpin them. We map stakeholder experiences with the competitive contracting policy onto relevant contracting and managed competition literatures. When measured against the goals of quality of care and efficiency, the findings presented here offer a mixed review of the experiences to date with the competitive contracting process introduced in Ontario's home care sector and suggest improvements for managing future competitive contracting processes.

Attitude of Health Personnel↗
PubMed2005

A modelling framework describing the enzyme regulation of membrane lipids underlying gradient perception in Dictyostelium cells II: input-output analysis.

Spatial sensing in Dictyostelium involves localization of the phosphoinositide lipids PI(3,4,5)P3 and PI(3,4)P2 at the leading edge of the cell in response to an external gradient. We have previously proposed a modelling framework describing the regulation of these lipids by the enzymes PI3K and PTEN. In this paper we analyse this regulation from an input-output perspective. When the inputs are homogeneous, we obtain explicit analytical expressions for the lipid concentrations as a function of enzyme concentrations and model parameters. We also show that the system can be cast as an open-loop bilinear control system, and employ control engineering tools to show that a local three-dimensional region in the four-dimensional phase space can be accessed by temporally varying either or both enzyme concentrations. For spatially graded enzyme profiles, we show that diffusion limits the extent to which lipid profiles can be manipulated by enzymes. However, we also demonstrate that for certain ranges of network parameters, increasing lipid diffusion can lead to an increase in steady-state leading-edge concentrations of PI(3,4,5)P3 or PI(3,4)P2, even though all lipid diffusion coefficients are equal. Finally, in order to determine the extent to which lipid profiles can be regulated by the enzymes, we formulate and solve inverse problems, where we determine the enzyme profiles required to realize particular lipid profiles at steady state.

Animals↗
PubMedDate not supplied

Self-organizing maps and clustering methods for matrix data.

In this contribution we present extensions of the Self Organizing Map and clustering methods for the categorization and visualization of data which are described by matrices rather than feature vectors. Rows and Columns of these matrices correspond to objects which may or may not belong to the same set, and the entries in the matrix describe the relationships between them. The clustering task is formulated as an optimization problem: Model complexity is minimized under the constraint, that the error one makes when reconstructing objects from class information is fixed, usually to a small value. The data is then visualized with help of modified Self Organizing Maps methods, i.e. by constructing a neighborhood preserving non-linear projection into a low-dimensional "map-space". Grouping of data objects is done using an improved optimization technique, which combines deterministic annealing with "growing" techniques. Performance of the new methods is evaluated by applying them to two kinds of matrix data: (i) pairwise data, where row and column objects are from the same set and where matrix elements denote dissimilarity values and (ii) co-occurrence data, where row and column objects are from different sets and where the matrix elements describe how often object pairs occur.

Cluster Analysis↗
PubMed2004

Speaking of weight: how patients and primary care clinicians initiate weight loss counseling.

BACKGROUND: Obesity is epidemic in the US and other industrialized countries and contributes significantly to population morbidity and mortality. Primary care physicians see a substantial portion of the obese population, yet rarely counsel patients to lose weight. METHODS: Descriptive field notes of outpatient visits collected as part of a multimethod comparative case study were used to study patterns of physician-patient communication around weight control in 633 encounters in family practices in a Midwestern state. RESULTS: Sixty-eight percent of adults and 35% of children were overweight. Excess weight was mentioned in 17% of encounters with overweight patients, while weight loss counseling occurred with 11% of overweight adults and 8% of overweight children. In weight loss counseling encounters, patients formulated weight as a problem by making it a reason for visit or explicitly or implicitly asking for help with weight loss. Clinicians did so by framing weight as a medical problem in itself or as an exacerbating factor for another medical problem. CONCLUSIONS: Strategies that increase the likelihood of patients identifying weight as a problem, or that provide clinicians with a way to "medicalize" the patient's obesity, are likely to increase the frequency of weight loss counseling in primary care visits.

Adult↗