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Results for “Problem Formulation”

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PubMed1995

[Therapeutic approaches in diseases caused by mycobacteria].

Following the historical introduction (the review by Schlossberger, 1928) the evolution of individual chemotherapy phases is briefly discussed. Then after following points are discussed. 1) The usual controlled clinical trials for evaluation of new drugs must be replaced (perhaps by estimates of the "early bactericidal activity" and of the 2 months' sputum conversion rates). 2) Interesting and of importance are research activities connected with the reasons for properties of TB bacilli in the persistence state, and of drugs capable to combat such bacilli (metronidazole?). 3) Since the human immunity against TB normally operates well (from 100 infected approximately 10 will get a clinically manifest disease), it is necessary to investigate possible combinations of chemo- and immunotherapy, either of combinations of antituberculous and immunomodulating drugs (eg. TNF alpha-antagonists), or of chemotherapy combined with vaccination (eg. M. vaccae). 4) There are still unsolved problems in formulations of drugs (particularly R in fixed combinations) and of drug resorption (in HIV-pos. patients). 5) Other points of research interest could be the adsorption of TB bacilli on the surface of mammalian cells (1st step in pathogenesis), drugs other than antituberculotics (eg. amoxycillin + clavulanic acid), or even drugs used for completely other diseases (eg. antidepressive). 6) All these attempts should serve primarily the purpose of further reduction of the necessary therapy duration (M+ pulmonary TB) to 1 - 2 months in total.

AIDS-Related Opportunistic Infections↗

PubMedDate not supplied

[Spike transmission in statistical neuron ensembles. III. Phase transition in a model of hippocampal field CA3].

The model consists of two types of neurons i. e. excitatory pyramidal cells and inhibitory basket ones. (the problem was formulated by Drs. O. S. Vinogradova and A. G. Bragin). The analysis of neuron activity has been carried out on the basis of "point approximation" of spikes transport equations. The graphs were obtained by computer. These graphs of the postsynaptic potentials averaged over ensemble are in good agreement with experimental data. The model observed demonstrates the phase transition over parameter characterizing the conduction of excitation between pyramidal cells. For weak pyramidal cells link there takes place the spontaneous activity regime. For strong link there were observed the epileptoid firing of neurons at 3 divided by 5 hertz and 140 divided by 240 msec phases of inhibition between bursts.

Hippocampus↗

PubMedDate not supplied

[Viral evolution: the development of the ecological trend in research].

A review of the main development stages of important components of the concept of viral evolution and ecological trends is given. The periods are distinguished by the time of discovery and studies of physicochemical and molecular genetic properties of the viruses, as well as the logic of penetration of general biology and ecology ideas in virology. On the basis of these processes, specific fundamental and applied problems were formulated and developed. Special attention is paid to transmission and preservation of viruses in populations, the role of civilization in development of novel infections, horizons, pathways of prophylaxis and future control of viruses.

Animals↗

PubMedDate not supplied

[Mathematical model of the bone callus tissue obtained during distraction osteosynthesis].

After some surgical interventions it's need to regenerate a part of bone. The new bone formation in the external fixation apparatus is the result of elongation and maturation of the bone callus, originated in pre-destructive period between bone fragments. The mathematical model of bone callus is proposed. Its main structural elements are osteogeneous and cartilage cells, osteoblasts, matrix, blood vessels. The derived equations take account of matrix production, dependent on the stress in tissue, and transformation of one kind of cells into another in accordance with O2 concentration is more or less than some critical value. The material of the callus is considered as a growing elastic body with growth coefficients, dependent on the structural tensor and Ca concentration. The structural tensor represents the anisotropy of fibrils orientation that take place during deformation. The concentrations of O2 and Ca are connected with the density of blood vessels whose propagation is related to the diffusion of a hypothetical substance. The formulated boundary problem allows to define changes in the growing zone of the callus and to define its size as a function of the rate of elongation.

Bony Callus↗

PubMedDate not supplied

[Illness rate with viral infections in the Russian Federation].

Presents data on the incidence of infections controllable by vaccine prevention, hepatitides, arbovirus infections, and hemorrhagic fevers, as well as on the share of virus infections in nosocomial morbidity. Defines the tasks of research and practical institutions in liquidation of poliomyelitis and decrease of the incidence of measles. Formulates the problems in epidemiology, prevention, and diagnosis of virus infections to be solved by the year 2000.

Humans↗

PubMed1993

Solvability of the electrocardiology inverse problem for a moving dipole.

New formulations of the direct and inverse problems for the moving dipole are offered. It has been suggested to limit the study by a small area on the chest surface. This lowers the role of the medium inhomogeneity. When formulating the direct problem, irregular components are considered. The algorithm of simultaneous determination of the dipole and regular noise parameters has been described and analytically investigated. It is shown that temporal overdetermination of the equations offers a single solution of the inverse problem for the four leads.

Algorithms↗

PubMed2001

Mind over matter? I: philosophical aspects of the mind-brain problem.

OBJECTIVE: To conceptualize the essence of the mind-body or mind-brain problem as one of metaphysics rather than science, and to propose a formulation of the problem in the context of current scientific knowledge and its limitations. METHOD AND RESULTS: The background and conceptual parameters of the mind-body problem are delineated, and the limitations of brain research in formulating a solution identified. The problem is reformulated and stated in terms of two propositions. These constitute a 'double aspect theory'. CONCLUSIONS: The problem appears to arise as a consequence of the conceptual limitations of the human mind, and hence remains essentially a metaphysical one. A 'double aspect theory' recognizes the essential unity of mind and brain, while remaining consistent with the dualism inherent in human experience.

Brain↗

PubMed1997

New finite difference formulations for general inhomogeneous anisotropic bioelectric problems.

Due to its low computational complexity, finite difference modeling offers a viable tool for studying bioelectric problems, allowing the field behavior to be observed easily as different system parameters are varied. Previous finite difference formulations, however, have been limited mainly to systems in which the conductivity is orthotropic, i.e., a strictly diagonal conductivity tensor. This in turn has limited the effectiveness of the finite difference, technique in modeling complex anatomies with arbitrarily anisotropic conductivities, e.g., detailed fiber structures of muscles where the fiber can lie in any arbitrary direction. In this paper, we present both two-dimensional and three-dimensional finite difference formulations that are valid for structures with an inhomogeneous and nondiagonal conductivity tensor. A data parallel computer, the connection machine CM-5, is used in the finite difference implementation to provide the computational power and memory for solving large problems. The finite difference grid is mapped effectively to the CM-5 by associating a group of nodes with one processor. Details on the new approach and its data parallel implementation are presented together with validation and computational performance results. In addition, an application of the new formulation in providing the potential distribution inside a canine torso during electrical defibrillation is demonstrated.

Algorithms↗

PubMed1988

The subacute hospital treatment of the borderline patient--I: An educational component.

Failure to begin the hospital treatment of the "borderline" patient with a formulation of the problems requiring hospitalization is an indication of a lack of integration in the staff's view of the patient's pathology. This failure may dovetail with a basic lack of integration in the patient's personality and recapitulate similar confusion and inconsistency within that patient's family. A 15-minute educational tape about "borderline" illness has been used to enhance integration and formulation of problems by staff and patients in a hospital setting in which stay is limited to one or two months. The program is described, and the taped programs included. "Self-regulatory disorder" is preferred to "borderline personality disorder." After one year's experience with the program, the staff has been better able to formulate difficulties in clinical discussions with patients and their families. The staff has noted a clearcut reduction of disruptive impulsive action in this population of hospitalized nonpsychotic patients.

Borderline Personality Disorder↗

PubMed2003

Arylazide cycloaddition to methyl propiolate: DFT-based quantitative prediction of regioselectivity.

Several 1(4-substituted)phenyl-4- or 5-methoxycarbonyl-1,2,3-triazoles have been synthesized by 1,3-dipolar cycloaddition of the corresponding arylazides to methyl propiolate in carbon tetrachloride. The regioselectivity of these reactions cannot be rationalized on the basis of the electronic demands of the reactants or frontier molecular-orbital theory. Therefore, we applied to this problem a quantitative formulation of the HSAB principle to this problem developed within density functional theory. Global and local reactivity indices were computed at B3LYP/6-311+G(d,p) level both in vacuo and in carbon tetrachloride (by the COSMO approach). The direction of charge transfer upon reactive encounter has been determined and the computed regioselectivity has been shown to be in good agreement with the experimental results. The relationship between computed and experimental data and how it is affected by the solvent have been discussed.

Journal Article↗

PubMed2002

Assignment strategy for proteins with known structure.

In protein NMR the assignment of nuclear spin resonances is a prerequisite for all subsequent applications, such as studies of ligand binding, protein-DNA interactions, and dynamics. Resonance assignment is a time consuming step even when the 3D x-ray structure of the protein is available. A new strategy is presented to solve the "inverse" assignment problem, which is the determination of the NMR resonance assignment from a known 3D protein structure. The protocol employs NMR data in the form of residual dipolar couplings and chemical shifts, while it does not require any sequential NMR connectivity information. The assignment problem is mathematically formulated in terms of a weighted matching problem that can be computationally efficiently solved by a combinatorial optimization algorithm. The protocol is applied to ubiquitin using two or three residual dipolar couplings per amino acid measured in Pfl phage medium together with chemical shift information. The algorithm yields for more than 90% of the protein backbone resonances the correct assignment.

Algorithms↗

PubMed1997

Mixed and Penalty Finite Element Models for the Nonlinear Behavior of Biphasic Soft Tissues in Finite Deformation: Part I - Alternate Formulations.

This paper addresses finite element-based computational models for the three-dimensional, (3-D) nonlinear analysis of soft hydrated tissues, such as the articular cartilage in diarthrodial joints, under physiologically relevant loading conditions. A biphasic continuum description is used to represent the soft tissue as a two-phase mixture of incompressible, inviscid fluid and a hyperelastic solid. Alternate mixed-penalty and velocity-pressure finite element formulations are used to solve the nonlinear biphasic governing equations, including the effects of a strain-dependent permeability and a hyperelastic solid phase under finite deformation. The resulting first-order nonlinear system of equations is discretized in time using an implicit finite difference scheme, and solved using the Newton-Raphson method. Using a discrete divergence operator, an equivalence is shown between the mixed-penalty method and a penalty method previously derived by Suh et al. [1]. In Part II [2], the mixed-penalty and velocity-pressure formulations are used to develop two-dimensional (2-D) quadrilateral and triangular elements and 3-D hexahedral and tetrahedral elements. Numerical examples, including those representative of soft tissue material testing and simple human joints, are used to validate the formulations and to illustrate their applications. A focus of this work is the comparison of alternate formulations for nonlinear problems. While it is demonstrated that both formulations produce a range of converging elements, the velocity-pressure formulation is found to be more efficient computationally.

Journal Article↗

PubMed1998

Mixed and Penalty Finite Element Models for the Nonlinear Behavior of Biphasic Soft Tissues in Finite Deformation: Part II - Nonlinear Examples.

This two-part paper addresses finite element-based computational models for the three-dimensional (3-D) nonlinear analysis of soft hydrated tissues, such as articular cartilage in diarthrodial joints, under physiologically relevant loading conditions. A biphasic continuum description is used to represent the soft tissue as a two-phase mixture of incompressible inviscid fluid and a hyperelastic, transversely isotropic solid. Alternate mixed-penalty and velocity-pressure finite element formulations are used to solve the nonlinear biphasic governing equations, including the effects of strain-dependent permeability and a hyperelastic solid phase under finite deformation. The resulting first-order, nonlinear system of equations is discretized in time using an implicit finite difference scheme, and solved using the Newton-Raphson method. Details of the formulations were presented in Part I [1]. In Part II, the two formulations are used to develop two-dimensional (2-D) quadrilateral and triangular elements and three-dimensional (3-D) hexahedral and tetrahedral elements. Numerical examples, including those representative of soft tissue material testing and simple human joints, are used to validate the formulations and to illustrate their applications. A focus of this work is the comparison of the alternate formulations for nonlinear problems. While it is demonstrated that both formulations produce a range of converging elements, the velocity-pressure formulation is found to be more efficient computationally.

Journal Article↗

PubMedDate not supplied

A system-structured medical record for intensive care patient documentation.

The problem-oriented approach to the medical record has aroused a long overdue interest in the structuring of the medical case file. Clinical information in the traditional record is source-structured and time-sequenced, whereas the problem-oriented system differs by being a problem-structured record retaining still a chronologic sequence. We have found that in acute illness the multiplicity of interacting pathophysiologic processes makes premature application of the problem-oriented approach cumbersome and unwieldy. The formulation of the problem list at an early stage often led to the reduplication of problems, creating disorder in the clinical picture rather than serving to clarify it. Some used the simple cataloguing of events and data as a substitute for clinical judgment and decision making, focusing more upon style rather than content of the medical record. By using a rigid physiologic system-structured "problem" list and a modification of the SOAP (Subjective Objective, Assessment, Plan) subdivision, we have improved the documentation of our intensive care patients. The summary of the patient's stay in the intensive care unit is structured with active and inactive problems, this summary to be further used as the permanent problem list.

Australia↗

PubMed2004

Separation of ion types in tandem mass spectrometry data interpretation -- a graph-theoretic approach.

Mass spectrometry is one of the most popular analytical techniques for identification of individual proteins in a protein mixture, one of the basic problems in proteomics. It identifies a protein through identifying its unique mass spectral pattern. While the problem is theoretically solvable, it remains a challenging problem computationally. One of the key challenges comes from the difficulty in distinguishing the N- and C-terminus ions, mostly b- and y-ions respectively. In this paper, we present a graph algorithm for solving the problem of separating bfrom y-ions in a set of mass spectra. We represent each spectral peak as a node and consider two types of edges: a type-1 edge connects two peaks possibly of the same ion types and a type-2 edge connects two peaks possibly of different ion types, predicted based on local information. The ion-separation problem is then formulated and solved as a graph partition problem, which is to partition the graph into three subgraphs, namely b-, y-ions and others respectively, so to maximize the total weight of type-1 edges while minimizing the total weight of type-2 edges within each subgraph. We have developed a dynamic programming algorithm for rigorously solving this graph partition problem and implemented it as a computer program PRIME. We have tested PRIME on 18 data sets of high accurate FT-ICR tandem mass spectra and found that it achieved ~90% accuracy for separation of b- and y- ions.

Algorithms↗

PubMed2003

Effects of experimental and modeling errors on electrocardiographic inverse formulations.

The inverse problem of electrocardiology aims to reconstruct the electrical activity occurring within the heart using information obtained noninvasively on the body surface. Potentials obtained on the torso surface can be used as input for the inverse problem and an electrical image of the heart obtained. There are a number of different inverse algorithms currently used to produce electrical images of the heart. The relative performances of these inverse algorithms at this stage is largely unknown. Although there have been many simulation studies investigating the accuracy of each of these algorithms, to date, there has been no comprehensive study which compares a wide variety of inverse methods. By performing a detailed simulation study, we compare the performances of epicardial potential [Tikhonov, Truncated singular value decomposition (TSVD), and Greensite] and myocardial activation-based (critical point) inverse simulations along with different methods of choosing the appropriate level of regularization (optimal, L-curve, composite residual and smoothing operator, zero-crossing) to apply to each of these inverse methods. We also examine the effects of a variety of signal error, material property error, geometric error and a combination of these errors on each of the electrocardiographic inverse algorithms. Results from the simulation study show that the activation-based method is able to produce solutions which are more accurate and stable than potential-based methods especially in the presence of correlated errors such as geometric uncertainty. In general, the Greensite-Tikhonov method produced the most realistic potential-based solutions while the zero-crossing and L-curve were the preferred method for determining the regularization parameter. The presence of signal or material property error has little effect on the inverse solutions when compared with the large errors which resulted from the presence of any geometric error. In the presence of combined Gaussian and correlated errors representing conditions which may be encountered in an experimental or clinical environment, there was less variability between potential-based solutions produced by each of the inverse algorithms.

Algorithms↗

PubMed2005

Minimum-time thermal dose control of thermal therapies.

The problem of controlling noninvasive thermal therapies is formulated as the problem of directly controlling thermal dose of the target. To limit the damage to the surrounding normal tissue, the constraints on the peak allowable temperatures in the selected spacial locations are imposed. The developed controller has a cascade structure with a linear, constrained, model predictive temperature controller in the secondary loop. The temperature controller manipulates the intensity of the ultrasound transducer with saturation constraints, which noninvasively heats the spatially distributed target. The main nonlinear thermal dose controller dynamically generates the reference temperature trajectories for the temperature controller. The thermal dose controller is designed to force the treatment progression at either the actuation or temperature constraints, which is required to minimize the treatment time. The developed controller is applicable to high and low-intensity treatments, such as thermal ablation and thermoradiotherapy. The developed approach is tested using computer simulations for a one-dimensional model of a tumor with constraints on the maximum allowable temperature in the normal tissue and a constrained power output of the ultrasound transducer. The simulation results demonstrate that the proposed approach is effective at delivering the desired thermal dose in a near minimum time without violating constraints on the maximum allowable temperature in healthy tissue, despite significant plant-model mismatch introduced during numerical simulation. The results of in vitro and in vivo validation are reported elsewhere.

Algorithms↗

PubMed1998

Health informatics and the humanities.

Researchers and professionals from the Humanities are new within the science of health informatics, where researchers and professionals from the natural sciences have so far de-fined the problems and their solutions. A cross-disciplinary collaboration can be difficult due to factors such as status and competition, to insufficient co-operation qualifications, and due to different definitions of problems. This paper presents examples of differently formulated health informatics problems. Cross-disciplinary collaboration is necessary but collaboration demands openness, curiosity, and readiness from researchers and professionals as well as it demands know-edge of the processes in cross-disciplinary cooperation. Considerations for cross-disciplines were actualized with the foundation in Denmark of the cross-disciplinary institution: The Virtual Centre for Health Informatics.

Cooperative Behavior↗