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Results for “Problem Formulation”

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At least 271 records · Page 15Linked to original sources

PubMed1994

Signal detection theory and reconstruction algorithms--performance for images in noise.

In many noisy image processing situations, decision making is the ultimate objective. In this paper, we show using signal detection theory how direct optimal processing of the projection data yields a considerable gain in the decision making performance over that obtained by first using image reconstruction. The problem is formulated in the framework of a two hypotheses detection problem. Optimal processors based on the likelihood ratio approach have been presented for two cases. The first considers direct processing of the projection data. The second applies optimal decision theory to the reconstructed data. Results based on computer simulation are presented in the form of receiver operating curves (ROCs) for different signal-to-noise (SNR) ratios. Early results indicate that large performance gains can be achieved by direct optimal processing of the projection data compared with optimal processing of reconstructed data. Results for the latter case can be interpreted as providing an upper bound on all postreconstruction decision rules. We hope to extend this approach to a number of different aspects of the image decision making problem.

Algorithms↗

PubMed2003

Determination of unsteady heat release distribution from acoustic pressure measurements: a reformulation of the inverse problem.

An integral method is developed to solve the inverse problem of determining the oscillatory heat release distribution from the knowledge of the acoustic pressure field within a combustor. Unlike earlier approaches, in which the problem is formulated in terms of Fredholm integral equation, the inverse problem is reformulated in terms of Volterra integral equation. This reformulation, valid for low Mach numbers (M2 << 1), facilitates the recovery of heat release at all frequencies. The resulting Volterra integral equation is solved using both direct numerical method and implicit least-squares method. The results show that the implicit least-squares method is superior to the direct numerical method and yields accurate determination of heat release at all frequencies.

Journal Article↗

PubMed1992

[Quality assurance in clinical trials. Problems related to patient information].

In connection with a phase-III study of cholesterol lowering agents, a questionnaire survey was carried out on information to patients' during clinical trials. The survey included 124 patients and nine team members with different professional backgrounds. The results show that, in spite of the fact that the patients had received information in accordance with the guidelines, only 47% of them had perceived that conventional treatment would be offered to those who dropped out of the study. A test of the extent of the patients' understanding about the drugs they were taking showed that only 39% knew how the drug acted and the reasons for the chosen dosing schedule. 23% of the patients would like to have received more information, but 9% of these had problems in formulating questions to the health personnel. Anxiety was a problem for 16% of patients, especially in the early phase of the clinical study. Only half of the team-members were aware of this. 45% of the patients felt that they would disappoint the team if they expressed a wish to drop out of the study. Most of the team-members would have tried to motivate the patients to continue to participate in the trial. Based on the results of the survey, we suggest some main elements of standard procedures for providing information to patients in connection with clinical trials.

Adult↗

PubMed1996

Health care reform and the role of public health agencies.

Experience in developing a local public health program, covering a period of approximately 45 years, is described. Included are the assessment and analysis of problems, policy formulation, plan development, and program implementation. A study of problems of seasonal farm workers, particularly those who migrate, is described, as well as a health services delivery program based on this study. Attention is given to incorporation of medical care with core public health services, and the use of a multidisciplinary team. Special features required to overcome cultural, language, educational, and other barriers are outlined. Adaption of knowledge gained from the migrant health project toward meeting needs of the county's medically underserved population is described. Involvement of the community, including representatives of private and public sectors, in the development and implementation of plans is emphasized. Maintaining appropriate emphasis on preventive aspects is discussed, together with mobilization of financial and other support. The importance of qualified public health staff is also emphasized: residency programs for physicians and dentists and training for other personnel are described.

Florida↗

PubMed2003

Synthesis and evaluation of PEG414, a novel formulating agent that avoids analytical problems associated with polydisperse vehicles such as PEG400.

Polyethylene glycol (PEG) 400 is widely used as a formulating agent for both intravenous and oral studies during drug discovery. It is a polydisperse material containing more than 16 oligomers, which can cause significant problems for high-performance liquid chromatography-mass spectrometry analysis due to ion suppression and isobaric interference. To overcome these difficulties, we have synthesized the single oligomer PEG414. The material has been characterized with a range of diverse drug compounds and shown to be comparable to PEG400 and superior to propylene glycol in terms of its solubilization power. The toxicological and metabolic properties of PEG414 should be similar to PEG400. It suffers none of the analytical problems associated with polydisperse agents and we expect it to be a useful alternative for the formulation of test compounds for intravenous and oral dosing during drug discovery.

Chemistry, Pharmaceutical↗

PubMed1989

Focal inpatient treatment planning.

Focal Inpatient Treatment Planning (FITP) is a new method of organizing and choosing among the many data available to the inpatient clinician. FITP emphasizes one Focal Problem, provides criteria for defining it, makes it possible to formulate the problem in operational language, channels free-ranging case discussion into workaday terms, invites the clinician to make explicit a sophisticated view of pathogenesis; including developmental, dynamic, and contextual factors, and ties formulation to intervention through explicit objectives. By requiring language that is jargon-free and accessible to patients and parents, FITP fosters empathy and alliance between the treatment community and the domain of the patient. This paper describes and illustrates FITP and provides guidelines for its implementation by an inpatient child and adolescent psychiatry service.

Adolescent↗

PubMedDate not supplied

[Lagrange formulation of the self-organization problem of a neuronal ensemble during computation of nonlinear dissipation of energy].

The Lagrange formulation for the problem of excitation of the Bresslow neural network is given to construct an arbitrary law for energy dissipation of the ensemble. The Amari assumption about neuron conductivity as a function of membrane potential allows one to admit the logistic dissipation law. It was shown that, from the viewpoint of statistics, this law is valid at coherent excitation conditions. The property of factorizing for the functioning of this ensemble was obtained.

Energy Metabolism↗

PubMed1977

General variational principles applicable to the hybrid element method.

Functional valued operators are used to formulate diffraction problems in a general abstract form. Variational principles for this formulation are developed. They are then applied to derive results on the linearized theory of free surface flows previously reported. Applications are also made to potential theory and elasticity.

Journal Article↗

PubMed2003

Examining outlying subjects and outlying records in bioequivalence trials.

The problem of detecting outliers in bioequivalence trials is considered. We formulate the problem as a hypothesis-testing problem under a mean-shift model and propose a test procedure based on the likelihood function. The test statistic has two components: one is to detect whether a specific pharmacokinetic measurement of a subject for certain formulation/drug product is an outlying value; the other is to test whether a subject as a whole is an outlying subject (with unusual high or low bioavailability for all formulations/drug products). Under normality assumption, the proposed procedure is most powerful. The small sample distribution of the proposed test statistic is derived. A numerical example illustrates the use of the procedure. The proposed test is then compared in a simulation study against the Hotelling T2 test, recommended by Liu and Weng (1991) for the use of outlier detection in bioequivalence studies. The results from the simulation study show that the proposed test is more powerful than the Hotelling T2 test.

Biological Availability↗

PubMed1982

On the relationship between resultant joint torques and muscular activity.

This paper is an investigation of the relationship between resultant joint torques and in vivo muscular activity. This relationship is currently inaccessible by direct experimental measurements due to the limited usefulness of electromyographic (EMG) data to indicate muscle force reliably and to proscriptions and experimental difficulties related to in vivo measurements on human subjects. The standard indirect method for inferring information about this relationship, using model studies in conjunction with temporal EMG data, is discussed. Key assumptions incorporated in these model studies, which lead to values for the joint force and torque resultants, are reviewed. The general distribution problem is formulated, and key assumptions associated with generating the simplified distribution problem that governs muscle activity are described. Two basically different methods for solving the simplified distribution problem and therefore determining the approximate relationship between resultant joint torques and muscular activity, including methods that attempt to account for the effect of antagonistic muscular activity, are discussed.

Biomechanical Phenomena↗

PubMed1979

Public choice in health: problems, politics and perspectives on formulating national health policy.

Development of health policy goals necessitates a choice among normative premises--an accommodation of conflicting values. Any debate that does not identify underlying assumptions or link policy prescriptions to a theoretical perspective is destined to degenerate into uncommunicative and unproductive rhetorical posturing. A sensible approach toward formulating national health policy requires that competing values be identified and discussed explicitly. This article will examine the effect that selection of different theoretical perspectives can have on the identification of problems and on the formulation of prescriptive policies in the health field. It will also focus on the different values that are promoted by different policy perspectives and consider alternative models for implementing value choices.

Attitude to Health↗

PubMed2004

Shape optimization of a cementless hip stem for a minimum of interface stress and displacement.

The primary stem stability is an essential factor for success of cementless hip stems. A correct choice of the stem geometry can improve the stem stability and, consequently, increase the life time of a hip implant. In this work, it is proposed a computational model for shape optimization of cementless hip stems. The optimization problem is formulated by the minimization of relative displacement and stress on bone/stem interface using a multi-criteria objective function. Also multiple loads are considered to incorporate several daily life activities. Design variables are parameters that characterize the geometry of selected cross sections, which are subject to geometric constraints to ensure a clinically admissible shape. The stem/bone set is considered a structure in equilibrium with contact conditions on interface. The contact formulation allows us to analyze different lengths of porous coating. The optimization problem is solved numerically by a steepest descent method. The interface stress and relative displacement are obtained solving the contact problem by the finite element method. Numerical examples are presented for a two-dimensional model of a hip stem, however, the formulation is general and can be applied to the three-dimensional case. The model gives indications about the relation between shape, porous coating and prosthesis stability.

Hip Prosthesis↗

PubMed2006

A theoretical formulation of the electrophysiological inverse problem on the sphere.

The construction of three-dimensional images of the primary current density (PCD) produced by neuronal activity is a problem of great current interest in the neuroimaging community, though being initially formulated in the 1970s. There exist even now enthusiastic debates about the authenticity of most of the inverse solutions proposed in the literature, in which low resolution electrical tomography (LORETA) is a focus of attention. However, in our opinion, the capabilities and limitations of the electro and magneto encephalographic techniques to determine PCD configurations have not been extensively explored from a theoretical framework, even for simple volume conductor models of the head. In this paper, the electrophysiological inverse problem for the spherical head model is cast in terms of reproducing kernel Hilbert spaces (RKHS) formalism, which allows us to identify the null spaces of the implicated linear integral operators and also to define their representers. The PCD are described in terms of a continuous basis for the RKHS, which explicitly separates the harmonic and non-harmonic components. The RKHS concept permits us to bring LORETA into the scope of the general smoothing splines theory. A particular way of calculating the general smoothing splines is illustrated, avoiding a brute force discretization prematurely. The Bayes information criterion is used to handle dissimilarities in the signal/noise ratios and physical dimensions of the measurement modalities, which could affect the estimation of the amount of smoothness required for that class of inverse solution to be well specified. In order to validate the proposed method, we have estimated the 3D spherical smoothing splines from two data sets: electric potentials obtained from a skull phantom and magnetic fields recorded from subjects performing an experiment of human faces recognition.

Algorithms↗

PubMed2005

Analysis of diffraction gratings by using an edge element method.

Typically the grating problem is formulated for TE and TM polarizations by using, respectively, the electric and magnetic fields aligned with the grating wall and perpendicular to the plane of incidence, and this leads to a one-field-component problem. For some grating profiles such as metallic gratings with a triangular profile, the prediction of TM polarization by using a standard finite-element method experiences a slower convergence rate, and this reduces the accuracy of the computed results and also introduces a numerical polarization effect. This discrepancy cannot be seen as a simple numerical issue, since it has been observed for different types of numerical methods based on the classical formulation. Hence an alternative formulation is proposed, where the grating problem is modeled by taking the electric field as unknown for TM polarization. The application of this idea to both TE and TM polarizations leads to a two-field-component problem. The purpose of the paper is to propose an edge finite-element method to solve this wave problem. A comparison of the results of the proposed formulation and the classical formulation shows improvement and robustness in the new approach.

Journal Article↗

PubMed2004

Ordered multiple-class ROC analysis with continuous measurements.

Receiver operating characteristic (ROC) curves have been useful in two-group classification problems. In three- and multiple-class diagnostic problems, an ROC surface or hyper-surface can be constructed. The volume under these surfaces can be used for inference using bootstrap techniques or U-statistics theory. In this article, ROC surfaces and hyper-surfaces are defined and their behaviour and utility in multi-group classification problems is investigated. The formulation of the problem is equivalent to what has previously been proposed in the general multi-category classification problem but the definition of ROC surfaces here is less complex and addresses directly the narrower problem of ordered categories in the three-class and, by extension, the multi-class problem applied to continuous and ordinal data. Non-parametric manipulation of both continuous and discrete test data and comparison between two diagnostic tests applied to the same subjects are considered. A three-group classification example in the context of HIV neurological disease is presented and the results are discussed.

AIDS Dementia Complex↗

PubMed2006

Dimer statistics on a Bethe lattice.

We discuss the exact solutions of various models of the statistics of dimer coverings of a Bethe lattice. We reproduce the well-known exact result for noninteracting hard-core dimers by both a very simple geometrical argument and a general algebraic formulation for lattice statistical problems. The algebraic formulation enables us to discuss loop corrections for finite dimensional lattices. For the Bethe lattice we also obtain the exact solution when either (a) the dimers interact via a short-range interaction or (b) the underlying lattice is anisotropic. We give the exact solution for a special limit of dimers on a Bethe lattice in a quenched random potential in which we consider the maximal covering of dimers on random clusters at site occupation probability p. Surprisingly the partition function for "maximal coverage" on the Bethe lattice is identical to that for the statistics of branched polymers when the activity for a monomer unit is set equal to -p. Finally we give an exact solution for the number of residual vacancies when hard-core dimers are randomly deposited on a one dimensional lattice.

Journal Article↗

PubMed2005

Tomographic fluorescence imaging in tissue phantoms: a novel reconstruction algorithm and imaging geometry.

A novel image reconstruction algorithm has been developed and demonstrated for fluorescence-enhanced frequency-domain photon migration (FDPM) tomography from measurements of area illumination with modulated excitation light and area collection of emitted fluorescence light using a gain modulated image-intensified charge-coupled device (ICCD) camera. The image reconstruction problem was formulated as a nonlinear least-squares-type simple bounds constrained optimization problem based upon the penalty/modified barrier function (PMBF) method and the coupled diffusion equations. The simple bounds constraints are included in the objective function of the PMBF method and the gradient-based truncated Newton method with trust region is used to minimize the function for the large-scale problem (39919 unknowns, 2973 measurements). Three-dimensional (3-D) images of fluorescence absorption coefficients were reconstructed using the algorithm from experimental reflectance measurements under conditions of perfect and imperfect distribution of fluorophore within a single target. To our knowledge, this is the first time that targets have been reconstructed in three-dimensions from reflectance measurements with a clinically relevant phantom.

Algorithms↗

PubMed1985

Custody and visitation. Problems and perspectives.

Child custody and visitation remain vexing problems requiring input from mental health professionals as public policy decisions are formulated. Difficult problems do not have easy solutions, but through continued exploration of the issues using clinical and research methods, perhaps innovative programs will be developed and evaluated. Ultimately, this may lead to better ways of helping families cope with the trauma and the consequences of the family break-up and the resulting attempt to establish custody and visitation.

Adaptation, Psychological↗