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PubMed1979

Tryptic proteolysis of coupling factor-latent ATPase from mycobacterium phlei. Theoretical modeling of structure-function relationships.

Trypsin treatment of solubilized coupling factor-latent ATPase from Mycobacterium phlei alters its subunit structure and functional properties. This coupling factor exhibits ATPase activity following trypsin treatment. Concurrently, both the ability of the enzyme to rebind to membranes depleted of coupling factor and its capacity for coupled phosphorylation are lost. The native alpha (64 000 dalton) subunit undergoes limited proteolytic digestion, and the delta (14 000 dalton) subunit is partially lost. During the course of tryptic proteolysis, the coupling factor molecule may exist in one of ten unique structural state (e.g. the native, ATPase-inactive molecule exists in the alpha alpha alpha state). Rigorous analysis of the experimental data by theoretical modeling provided information concerning the intermediate structural states leading to the fully ATPase-activated alpha" alpha" alpha" state under different conditions of trypsin treatment. The theoretical models of structure-function relationships that best-represented the experimental data predicted that the native coupling factor molecule contains three copies of the alpha (64 000 dalton) form of the alpha subunit, that the alpha" (58 000 dalton) alpha subunit species contributes maximally and the alpha' (61 000 dalton) form about half-maximally to ATPase activity, that membrane rebinding ability is proportional to the number of native alpha subunits in the enzyme, and that at least one native alpha subunit/molecule is required for full expression of coupled phosphorylation. These results indicate an essential role for the alpha subunit in the regulation of ATPase activity and in the ability of the solubilized coupling factor to rebind to depleted membranes.

Adenosine Triphosphatases↗

PubMed2005

Theoretical models and analytic expressions for buildup time of pulsed confocal unstable optical parametric oscillators with uniform or Gaussian reflectivity mirrors.

A theoretical model and a simplified analytic expression are developed to describe the buildup time of a pulsed confocal unstable optical parametric oscillator (OPO) with a uniform-reflectivity mirror (URM) or a Gaussian-reflectivity mirror (GRM). Two analytic expressions have been demonstrated to correspond to theoretical models with a sufficient degree of accuracy. The effects of a variety of cavity and pump parameters on the buildup time of an OPO were investigated and analyzed. It was found that a GRM unstable OPO generally exhibits a shorter buildup time than the corresponding URM unstable OPO with equally effective output coupling.

Journal Article↗

PubMed1983

Theoretical modeling of filtration of blood cell suspensions.

A theoretical model of filtration of suspensions containing red blood cells (RBCs) and white blood cells (WBCs) has been developed. Equations are written for the pressure drop, the filtration flow and the fractions of filter pores containing RBCs (alpha) and WBCs (alpha*). Because the relative resistances (ratios of resistance of cell to resistance of suspending fluid) of RBCs (beta) and WBCs (beta*) through the filter pore are greater than one, the transit of these cells (especially WBCs) through the filter is slower than that of suspending fluid; this leads to values of alpha and alpha* higher than those simply expected from the hematocrit and leukocrit, respectively, in the entering and exiting suspensions. In the absence of pore plugging by the cells (steady flow), the pressure drop can be computed from alpha, alpha*, beta and beta*. In order to model unsteady flow, differential equations are written to include pore plugging and the subsequent unplugging by the rising filtration pressure at a constant flow. By specifying the fractions of entering RBCs (epsilon) and WBCs (epsilon*) which would plug the pores and the rate at which the plugged pores would unplug in response to pressure rise (epsilon u), as well as the fractions of entering RBCs (epsilon p) and WBCs (epsilon p*) that would plug the pores permanently, theoretical pressure-time curves can be generated by numerical integration, and the results fit the experimental data well. From such fitting of theoretical curve to experimental data, information can be deduced for epsilon, epsilon*, epsilon u, epsilon p and epsilon* p.

Erythrocytes↗

PubMed1991

[Humoral cycle as a mechanism providing autoregulation of the processes of the immune system (theoretical model)].

The author presents a hypothesis on a possible mechanism of autoregulation of the immune response maturation in simulated influenza. A theoretical model describing a cyclic process of so-called "humoral cycle" which provides a directed selection of immunocompetent cells' clones and physiologic limitation of cytotoxic reactions. Possible features of humoral cycle function are considered in the concrete experimental examples. The author demonstrated possible mechanisms of immunological barrier violation in synthesis of big amounts of high affinity + antibodies to antigens of causative agent. Possible application of the theoretical model suggested in immunological studies is considered.

Animals↗

PubMedDate not supplied

Use of a Western theoretical model to investigate the relationships among characteristics of pregnant women, utilization, and satisfaction with prenatal care services in St. Petersburg, Russia.

Few studies of utilization and satisfaction with prenatal care services have been conducted internationally. In this study, utilization and satisfaction with prenatal care services in St. Petersburg, Russia were examined using Aday and Andersen's (1974) A Framework for the Study of Access to Medical Care. This study was conducted under the auspices of the European Region, World Health Organization (WHO) Healthy Cities Project, which promotes a community-based intersectoral approach to meeting health needs. The convenience sample included 397 women with uncomplicated pregnancies and normal deliveries, representing an 86% response rate. Multiple regression and path analysis found significant predictors of prenatal care utilization and satisfaction. They were different, however, from those posited in the theoretical model. This indicates that Aday and Andersen's health care services model is specific to the U. S. health care system, where it originated. The Russian health care system has been and remains different from that of the United States. If the reformed Russian health care system takes on aspects of the U. S. health care system, the utility of Aday and Andersen's theoretical model may change.

Adolescent↗

PubMed1992

Leukemic progression as process of adaptation (theoretical model).

On the basis of an assumption that leukemic progression is a process of adaptation of normal hemopoiesis to the effect of the leukemic clone, a theoretical model of leukemia development is built. General conclusions are as follows: the possibility of reaching remission depends upon suppression of normal hemopoiesis by cytostatics in a system of two cell populations: the duration of remission depends upon suppression of the leukemic clone; the quantity of blast cells of marrow in remission can exceed 5 per cent.

Adaptation, Physiological↗

PubMed1987

The life sciences in nursing: development of a theoretical model.

This paper explores the relationship between the life sciences of anatomy, physiology, microbiology and pharmacology and the teaching/learning problems of their application in nursing. A theoretical model is proposed derived from a conceptual consideration of nursing tasks and of nursing actions developed to account for a direct link between these sciences and nursing. It is argued that a 'bio-nursing' approach to the use of the life sciences in nursing is comparable to that of a 'bio-medical' approach in medical education and practice. The paper suggests that an appropriate examination of the contributions of the life sciences to nursing education will provide a more concentrated and illuminating exercise with regard to making possible the identification of a body of knowledge of direct relevance to nursing practice. The teaching/learning implications for nurse education and the development of a distinctive knowledge base derived from these sciences are discussed.

Biology↗

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↗

PubMed2000

A theoretical model for the prediction of sequence-dependent nucleosome thermodynamic stability.

A theoretical model for predicting nucleosome thermodynamic stability in terms of DNA sequence is advanced. The model is based on a statistical mechanical approach, which allows the calculation of the canonical ensemble free energy involved in the competitive nucleosome reconstitution. It is based on the hypothesis that nucleosome stability mainly depends on the bending and twisting elastic energy to transform the DNA intrinsic superstructure into the nucleosomal structure. The ensemble average free energy is calculated starting from the intrinsic curvature, obtained by integrating the dinucleotide step deviations from the canonical B-DNA and expressed in terms of a Fourier series, in the framework of first-order elasticity. The sequence-dependent DNA flexibility is evaluated from the differential double helix thermodynamic stability. A large number of free-energy experimental data, obtained in different laboratories by competitive nucleosome reconstitution assays, are successfully compared to the theoretical results. They support the hypothesis that the stacking energies are the major factor in DNA rigidity and could be a measure of DNA stiffness. A dual role of DNA intrinsic curvature and flexibility emerges in the determination of nucleosome stability. The difference between the experimental and theoretical (elastic) nucleosome-reconstitution free energy for the whole pool of investigated DNAs suggests a significant role for the curvature-dependent DNA hydration and counterion interactions, which appear to destabilize nucleosomes in highly curved DNAs. This model represents an attempt to clarify the main features of the nucleosome thermodynamic stability in terms of physical-chemical parameters and suggests that in molecular systems with a large degree of complexity, the average molecular properties dominate over the local features, as in a statistical ensemble.

Base Sequence↗

PubMed1991

A theoretical model of gas transport between arterioles and tissue.

A theoretical model of CO2 and O2 diffusion between arterioles and tissue was developed to determine if significant transport could occur in precapillary vessels. There is increasing evidence, both theoretical and experimental, that such exchange does occur. Using a model in which CO2 and O2 were coupled through the Bohr and Haldane effects, we quantified the radial and axial transport. We also examined the roles of axial diffusion in the arteriole wall and tissue and capillary structure on the transport. Capillary arrangements investigated included capillaries independent of the arteriole with the entering capillary PCO2 or PO2 equal to a constant, and capillaries branching off along the length of the arteriole with the entering capillary partial pressure equal to the arteriole partial pressure at the given axial location. We found that for CO2 in arterioles with an inner diameter ranging from 200 to 22 microns, the exiting blood was 6 to 45% of the way to complete equilibrium with the surrounding tissue, respectively. For O2, the range was 8 to 25%, respectively. We also determined that axial diffusion in the arteriole wall and tissue has little effect on the transport and that capillary structure can alter tissue PCO2 by as much as 12 mm Hg in the smallest arteriole, but has little effect on O2 transport.

Arterioles↗

PubMed2006

Theoretical model of reticulocyte to erythrocyte shape transformation.

A theoretical model describing the kinetics of reticulocyte shape transformation was developed. The model considers the evolution of a simple cellular shape under transmembrane pressure difference, and proposes a four-parameter axisymmetric approximation of the cell surface. The mathematical analysis considers plasma membrane tension in the plane of bilayer leaflets, membrane spontaneous curvature and transmembrane transport of water. Cytoskeleton dilatational and shear rigidity, and the energetic barrier preventing the decrease of cell volume below a certain minimum are also incorporated. The set of adequate physical assumptions allowed for formulation of the equation for free energy of the investigated system. Computer simulations of cell shape changes, down to the state of free energy minimum, together with estimation of the time needed for the resulting transport of water, revealed a complex, three-phase picture of temporal alterations in cellular geometry with a wide spectrum of final results, and led to propose a standard model of reticulocyte-erythrocyte transformation. According to the model, both cell volume and surface undergo changes, and the work of the pressure, initially accumulated in the cytoskeleton, is consumed for local bending of the cell membrane. Further simulations with modified initial shape or parameters of the standard model show the trajectories of system evolution and help in better understanding the conditions for the erythro-, sphero-, ovalo-, stomato-, and leptoidal metamorphosis of maturing red blood cells. The stability of the final biconcave shape was also verified. Spherogenic modifications were discussed in the context of spherocytosis. Future development of the model was proposed.

Cell Differentiation↗

PubMedDate not supplied

A theoretical model of social consciousness.

The article presents a theoretical model of social consciousness developed from nurses' life histories. A 3-position dialectical framework--acquired, awakened, and expanded social consciousness--makes visible the way people respond to social injustice in their lives and in the lives of others. The positions coexist, are not hierarchical, and are contextually situated. A person's location influences her or his availability for social action. Nurses who could most contribute to challenging social injustices that underpin health disparities are relegated to the margins of mainstream nursing by internal processes of discrimination. More inclusive definitions of "a nurse" would open up possibilities for social change.

Adult↗

PubMed1994

The road not taken: an integrative theoretical model of reading disability.

This article describes a theoretical model of reading disability that integrates a wide range of research findings in cognitive psychology, reading, and education across the age and grade span. The model shows how reading disability relates to normal reading acquisition, and includes four possible patterns of reading disability: nonalphabetic readers, compensatory readers, nonautomatic readers, and readers delayed in the acquisition of word-recognition skills. We compare our model to the models of other investigators and argue that our model is especially useful to practitioners. Finally, we discuss some of the educational implications of the model.

Adolescent↗

PubMed1998

A theoretical model to predict distribution of the fabric tensor and apparent density in cancellous bone.

The adaptation of cancellous bone to mechanical forces is well recognized. Theoretical models for predicting cancellous bone architecture have been developed and have mainly focused on the distribution of trabecular mass or the apparent density. The purpose of this study was to develop a theoretical model which can simultaneously predict the distribution of trabecular orthotropy/orientation, as represented by the fabric tensor, along with apparent density. Two sets of equations were derived under the assumption that cancellous bone is a biological self-optimizing material which tends to minimize strain energy. The first set of equations provide the relationship between the fabric tensor and stress tensor, and have been verified to be consistent with Wolff's law of trabecular architecture, that is, the principal directions of the fabric tensor coincide with the principal stress trajectories. The second set of equations yield the apparent density from the stress tensor, which was shown to be identical to those obtained based on local optimization with strain energy density of true bone tissue as the objective function. These two sets of equations, together with elasticity field equations, provide a complete mathematical formulation for the adaptation of cancellous bone.

Bone Density↗

PubMed1990

Theoretical models and prediction of the changes in case mortality patterns in major Chinese cities.

"Through a comparison of different methods, this study is intended to set up more satisfactory theoretical models of case mortality patterns in major Chinese cities, to ascertain the manner of changes in the time sequence of various diseases, and to predict the trends of these changes. This study is based on the data of causes of death in the country's 14 cities having a population of over one million, where there are complete statistical registration systems and reliable data."

Cause of Death↗

PubMed1979

[The borderline syndrome: conceptual problem, theoretical models, nosographic location].

The historical vicissitudes of the term "borderline" in psychiatric literature as well as its actual conceptual dimension are reviewed. The latter is exposed organized in categories or theoretical models as follows: as a peculiar or attenuate presentation of a psychosis, a grave form of a neurosis, a passage syndrome between a neurosis and a psychosis, or an independent nosographic picture. In mentioning pathochronic and generic aspects, an intent of unitary conceptualization is outlined which comprises: I) the clinical picture which translates ego pathology into behavioral terms with a "longitudinal" symptomatological hierarchization of functional levels which interact simultaneously sometimes (dynamic psychopathological space-time) and pointing out its dependence on the environment; II) the structural analysis or the dynamic formulation. The actual nosographic position of the borderline syndrome as well as the one established in the proposed Third Review of the American Psychiatric Classification and its heuristic value are examined. Finally, the presence of this syndrome in relation to modern time society characteristics is commented.

Humans↗

PubMed2006

Theoretical model of intravascular paramagnetic tracers effect on tissue relaxation.

The concentration of MRI tracers cannot be measured directly by MRI and is commonly evaluated indirectly using their relaxation effect. This study develops a comprehensive theoretical model to describe the transverse relaxation in perfused tissue caused by intravascular tracers. The model takes into account a number of individual compartments. The signal dephasing is simulated in a semianalytical way by embedding Monte Carlo simulations in the framework of analytical theory. This approach yields a tool for fast, realistic simulation of the change in the transverse relaxation. The results indicate that the relaxivity of intravascular contrast agents depends significantly on the host tissue. This agrees with experimental data by Johnson et al. (Magn Reson Med 2000;44:909). In particular, the present results suggest a several-fold increase in the relaxivity of Gd-based contrast agents in brain tissue compared with bulk blood. The enhancement of relaxation in tissue is due to the contrast in magnetic susceptibility between blood vessels and parenchyma induced by the presence of paramagnetic tracer. Beyond the perfusion measurements, the results can be applied to quantitation of functional MRI and to vessel size imaging.

Cell Membrane↗

PubMedDate not supplied

Selectional constraints: an information-theoretic model and its computational realization.

A new, information-theoretic model of selectional constraints is proposed. The strategy adopted here is a minimalist one: how far can one get making as few assumptions as possible? In keeping with that strategy, the proposed model consists of only two components: first, a fairly generic taxonomic representation of concepts, and, second, a probabilistic formalization of selectional constraints defined in terms of that taxonomy, computed on the basis of simple, observable frequencies of co-occurrence between predicates and their arguments. Unlike traditional selection restrictions, the information-theoretic approach avoids empirical problems associated with definitional theories of word meaning, accommodates the observation that semantic anomaly often appears to be a matter of degree, and provides an account of how selectional constraints can be learned. A computational implementation of the model "learns" selectional constraints from collections of naturally occurring text; the predictions of the implemented model are evaluated against judgments elicited from adult subjects, and used to explore the way that arguments are syntactically realized for a class of English verbs. The paper concludes with a discussion of the role of selectional constraints in the acquisition of verb meaning.

Adult↗