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At least 667 records · Page 37Linked to original sources
PubMed1992

Transition to being the mother of a new infant in the first 3 months: maternal problem solving and self-appraisals.

This study explored components of a model of transition to being the mother of a new infant during an infant's first 3 months. Personal and situational conditions and maternal problem-solving factors (issue formulating and the use of help with issues) that may influence transition markers (maternal appraisal of problem-solving competence and evaluation of parenting) were examined for two study periods: the first 30 days postpartum and the next 60 days. For the second study period, variables contributing to maternal attention to infant growth, development and temperament (knowing issues) were also explored. Questionnaires and a daily log kept by 62 mothers of healthy term infants were data sources. Everyday supports (situational condition) contributed to use of lay help for the second period. Caretaking issues positively influenced use of clinician help throughout the study. The number of knowing issues a mother formulated contributed positively to problem-solving competence and to parenting evaluation; the use of problem-solving help had no effect. More clinician help received during the first month meant higher need for maternal action for both knowing and caretaking issues in the second and third months. Further study of the mechanisms of these relationships and examination of factors contributing to shifts in the transition process are needed.

Adult↗
PubMed1991

Temporal-abstraction mechanisms in management of clinical protocols.

We have identified several general temporal-abstraction mechanisms needed for reasoning about time-stamped data, such as are needed in management of patients being treated on clinical protocols: simple temporal abstraction (a mechanism for abstracting several parameter values into one class), temporal inference (a mechanism for inferring sound logical conclusions over a single interval or two meeting intervals), and temporal interpolation (a mechanism for bridging non-meeting temporal intervals). Making explicit the knowledge required for temporal abstractions supports the acquisition of planning knowledge, the identification of clinical problems, and the formulation of clinical-management-plan revisions.

Clinical Protocols↗
PubMed2002

On the degeneracy of the IMRT optimization problem.

One approach to the computation of photon IMRT treatment plans is the formulation of an optimization problem with an objective function that derives from an objective density. An investigation of the second-order properties of such an objective function in a neighborhood of the minimizer opens an intuitive access to many traits of this approach. A general finding is that only a small subset of the parameter space has nonzero curvature, while the objective function is entirely flat in a neighborhood of the minimizer in most directions. The dimension of the subspace of vanishing curvature serves as a measure for the degeneracy of the solution. This finding is important both for algorithm design and evaluation of the mathematical model of clinical intuition, expressed by the objective function. The structure of the subspace of great curvature is found to be imposed on the problem by conflicts between objectives of target and critical structures. These conflicts and their corresponding modes of resolution form a common trait between all reasonable treatment plans of a given case. The high degree of degeneracy makes the use of a conjugate gradient optimization algorithm particularly favorable since the number of iterations to convergence is equivalent to the number of different eigenvalues of the curvature tensor and is hence independent from the number of optimization parameters. A high level of degeneracy of the fluence profiles implies that it should be possible to stipulate further delivery-related conditions without causing severe deterioration of the dose distribution.

Algorithms↗
PubMed1992

Channelling of controlled release formulation of ketoprofen (Oscorel) in patients with history of gastrointestinal problems.

STUDY OBJECTIVE: The aim was to determine if a new controlled release formulation (Oscorel) of the non-steroidal anti-inflammatory drug (NSAID) ketoprofen has been preferentially prescribed in patients with prior history of gastro-intestinal disturbances. DESIGN: The study was a pharmacy records based comparison of the rates of prior prescribing of drugs indicated for peptic ulcer treatment in first recipients of Oscorel in 1989 versus recipients of other NSAID products. SETTING: A representative panel of Dutch community pharmacies serving approximately 425,000 people was used. MAIN RESULTS: Oscorel was launched in January 1989. Data on prescriptions dispensed in 1987-1988 to a total of 837 first users of Oscorel were analysed and compared with the dispensing history of a reference population including 30,787 patients who did not receive a prescription for Oscorel during 1989. Compared to the reference population, first users of Oscorel included a greater proportion of females, of patients 75 years and older, of heavy users of NSAIDs, and of patients switching among different NSAIDs. A total of 24.1% of first users of Oscorel had received peptic ulcer therapy in 1987-1988, versus 15.7% of the reference population. The rate ratio was 1.54, with 95% confidence interval of 1.36-1.74. Adjustment for stratifying variables caused only minor changes in the rate ratio, which remained stable on 1.5. CONCLUSIONS: Oscorel appears to have been channelled into use in patients with recognised risk factors for gastrointestinal toxicity. This preferential prescribing probably resulted from expectations and claims that this product has a lower risk of such toxicity.

Community Pharmacy Services↗
PubMedDate not supplied

[Management of malnutrition in preschool children: the role of primary health care services].

Although the prevalence of malnutrition in developing countries is decreasing, it is still a major problem for many children under five. As socio-economic conditions are the main determinants, a final solution for this problem can only be envisaged in the long run. Still, short-term strategies need to be defined in order to relieve the sufferings of individual children and their families. Understanding the problem and consequently formulating intervention programs at the local level remains a complex and difficult issue. The first reason being that the process of malnutrition expresses itself in different forms and with variable consequences. A second reason making malnutrition a complex problem is that the primary causes -- the interaction between insufficient food supply and the frequent recurrence of infectious diseases -- are determined by a multitude of factors of different natures. This complexity -- of its expressions, effects, and causality -- makes it difficult to get a global vision and understanding of the problem, which clearly impedes the definition of rational and integrated intervention strategies. Nevertheless, a better understanding of the pathophysiology of malnutrition and of the factors that influence the growth process in preschool age, will help to better direct actions. To this effect, a conceptual model will be built, based on recent insight in the process of malnutrition within this age group. From this model, two lines of action for increasing the chances of preschool children to express their initial growth potential, become apparent. A first series of activities could tackle the process that, via wasting and recurrence of infections, leads to an increased mortality risk. As timely intervention reduces the risk of depletion of energy reserves, these activities would also have an indirect impact on physical development. Elaborating strategies for secondary prevention and for treating severe cases belongs to the specific competence of the health sector. In the second line of action, the aim is to intervene before reserves are depleted. Here, primary prevention and health promotion are choice activities. This frame of reference will be used for analysing existing health programs for preschool children and how they propose to improve the management of malnutrition. This analysis will show that primary health care services can play a much more important role than usually attributed to them. Identifying these gaps and elaborating alternatives is the purpose of this article.

Child Development↗
PubMed1991

Thickness extrema at the edge of shaped lenses: the general problem and the solution for a straight edge obtained by means of direct elimination and of Lagrange multipliers.

In general thickness varies along the cut edge of a lens. There is some interest in being able to predict the locations of the thickest and thinnest points on the edge. One purpose of this paper was to formulate the general problem mathematically of finding the locations of thickness extrema on the edge of an arbitrary lens cut into an arbitrary shape. A second purpose was to illustrate how the problem can be solved. In particular, the problem is solved completely and explicitly for what is probably the simplest case, the straight cut edge. A component-free matrix expression for the position of the extremum is derived by employing Lagrange multipliers and the concept of the generalized inverse of a matrix. The equation applies to spheres, cylinders and sphero-cylinders and allows for the presence of prism as well. Along some edges the thickness is constant. Along other edges the thickness varies linearly; there are no extrema except for the practical extrema at the two ends of the edge: thickest at the one and thinnest at the other. The mathematical conditions for these two cases are presented. Equivalent to the matrix equation for the position vector of the thickness extremum is a pair of scalar equations expressed in terms of components of the matrices. The pair is useful when locating extrema using manual calculations. On the other hand, the component-free matrix equation is useful in other circumstances such as for mathematical manipulations and when using computer software that handles matrices. The former is used in a number of numerical examples; the latter was used to check the answers by computer. The mathematical techniques described here are likely to find application in other areas of ophthalmic and visual optics.

Lenses↗
PubMed1978

Basilar membrane motion in a spiral-shaped cochlea.

To examine the influence of the spiral coiling of the cochlea upon the motion of the basilar membrane, a mathematical model of the cochlea is constructed. The formulation of the problem leads to Laplace's equation in three dimensions in a curvilinear coordinate system plus corresponding boundary conditions. By basing the choice of the coordinate system upon the form of the helix representing the centerline of the basilar membrane, a relatively simple formulation is obtained. The helix parameters appear only in the Laplacian, not in the boundary conditions. From experimental data the equations of the basilar membrane's centerline are derived for a human cochlea, both in intrinsic form and in regular form. The relative simplicity of the formation permits the tentative conclusion that, in spite of the large curvature near the apex, the spiral shape of the cochlea has only a small influence upon the motion of the basilar membrane.

Basilar Membrane↗
PubMedDate not supplied

[Flight problems in Soviet aviation medicine in the 1920s and 1930s].

This paper describes multifaceted investigations of the flying work by Soviet aviation medicine in the 1920-30s. It examines the early stages of the professional activity that is at present termed ergonomic foundations of the design, manufacture and use of the aircraft. The paper discusses one of the first formulations of the problem of standardization of the human factors.

Aerospace Medicine↗
PubMed1980

Problems and hypotheses.

The formulation and relationship of precisely defined research questions and hypotheses and their importance in the research process are discussed. A hypothesis is defined as a linkage of two or more abstract variables, each of which is derived from the observational level. The successive abstractions of the derivation process, the characteristics of the variables so derived, and the relationship of both to study design and measurement are defined and discussed.

Abstracting and Indexing↗
PubMed2003

A novel linear programming approach to fluence map optimization for intensity modulated radiation therapy treatment planning.

We present a novel linear programming (LP) based approach for efficiently solving the intensity modulated radiation therapy (IMRT) fluence-map optimization (FMO) problem to global optimality. Our model overcomes the apparent limitations of a linear-programming approach by approximating any convex objective function by a piecewise linear convex function. This approach allows us to retain the flexibility offered by general convex objective functions, while allowing us to formulate the FMO problem as a LP problem. In addition, a novel type of partial-volume constraint that bounds the tail averages of the differential dose-volume histograms of structures is imposed while retaining linearity as an alternative approach to improve dose homogeneity in the target volumes, and to attempt to spare as many critical structures as possible. The goal of this work is to develop a very rapid global optimization approach that finds high quality dose distributions. Implementation of this model has demonstrated excellent results. We found globally optimal solutions for eight 7-beam head-and-neck cases in less than 3 min of computational time on a single processor personal computer without the use of partial-volume constraints. Adding such constraints increased the running times by a factor of 2-3, but improved the sparing of critical structures. All cases demonstrated excellent target coverage (> 95%), target homogeneity (< 10% overdosing and < 7% underdosing) and organ sparing using at least one of the two models.

Algorithms↗
PubMed2001

A case-acquisition and decision-support system for the analysis of group-average lactation curves.

A case-acquisition and decision-support system was developed to support the analysis of group-average lactation curves and to acquire example cases from domain specialists. This software was developed through several iterations of a three-step approach involving 1) problem analysis and formulation in consultation with two dairy nutrition specialists; 2) development of a case-acquisition and decision-support prototype by the system developer; and 3) use of the prototype by the domain specialists to analyze and classify milk-recording data from example herds. The overall problem was decomposed into three subproblems: removal of outlier tests and lactation curves of individual cows; interpretation of group-average lactation curves; and diagnosis of detected abnormalities at the herd level through the identification of potential management deficiencies. For each subproblem, a software module was developed allowing the user to analyze both graphical and numerical performance representations and classify these representations using predefined linguistic descriptors. The example-based method for the development of the program proved to be very useful, facilitating the communication between system developer and domain specialists, and allowing the specialists to explore the appropriateness of the various prototypes developed. The resulting software represents a formalization of the approach to group-average lactation curve analysis, elicited from the two domain specialists. In future research, the case-acquisition and decision-support system will be complemented with knowledge to automate identified classification tasks, which will be captured through the application of machine-learning techniques to example cases, acquired from domain specialists using the software.

Animals↗