Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Systems Theory”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41Linked to original sources
PubMed1979

Ecosystemic epistemology: an alternative paradigm for diagnosis.

An alternative paradigm for diagnosis based on cybernetics, ecology, and systems theory is proposed. This paradigm, termed "ecosystemic epistemology," suggests that diagnosis focus on knowing problematic situations in an ecological and systemic way. Theoretical statements concerning this approach are delineated with specific references to major family therapists. This discussion provides a foundation for an ecosystemic epistemology for diagnosis that addresses the following issues: (a) the meaning of system; (b) the symptom's presence in the system; (c) the therapist's presence in the system; (d) the ecological relationship system that emerges in diagnosis; and (e) the relation between ecosystemic epistemology and the process of diagnosis. In effect, this paper attempts to formally describe the underlying epistemology inherent in the work of therapists who approach diagnosis in an ecological and systemic way.

Cultural Characteristics↗
PubMed2005

Peer relationships and psychopathology in developmental perspective: reflections on progress and promise.

Articles in this special section illuminate progress, challenges, gaps, and future directions for theory and research concerned with peer relations and psychopathology. Advances reflect the emergence of developmental psychopathology, with its emphasis on systems theory, dynamic interactions of individuals in context, processes and change, complexity, integration of normative and pathological development, and longitudinal designs. Gaps reflect the challenges and exciting future ahead for research on peer processes in developmental psychopathology across multiple levels of analysis.

Adolescent↗
PubMed1978

[Coronary autoregulation of the isolated rabbit heart].

The autoregulation behaviour of the coronary circulation was studied on an isolated Langendorff-heart of rabbit. Static pressure-flow curves were recorded for the normal and maximally dilated vascular system. For analyzing the dynamics of autoregulation of the flow to pressure jumps within the autoregulation range was measured. Modelling was performed by means of the linear system theory, assuming first-order transfer functions for the contraction and dilatation process co-acting in the regulation. The system parameters were determined in the time-range by adapting a bi-exponential function to the measured data. For the dilatation reaction following pressure fall a mean time constant of 5.4 s was measured, while a time constant of 146.8 s was found for the counterregulation (constriction). These events are discussed with regard to possible further studies on the pharmacology of coronary regulation.

Animals↗
PubMed1989

Constraints among molecular and systemic properties: implications for physiological genetics.

Physiological genetics attempts to relate the molecular genetic properties of an organism--the genotype--to its integrated or physiological behavior--the phenotype. There has been relatively little progress in this field when compared to the neighboring fields of molecular and population genetics. This is due in part to the large number of highly non-linear interactions that characterize such systems. Biochemical Systems Theory is one approach that shows promise in dealing with the large number of non-linear interactions in a systematically structured manner. A variant of this approach has stressed the use of specific mathematical constraints, called summation and connectivity relationships, among molecular and systemic properties. In particular, the summation relationship has been used to argue that the predominance of recessive mutations is the inevitable consequence of the kinetic structure of enzyme networks and need not be attributed to natural selection. In order to put in broader perspective the implications of such constraints for physiological genetics, we have presented in this paper the outlines of the larger theory and the set of generalized steady state constraints that follow from first principles within this theory. The results show that the summation relationship suffers from a number of fundamental limitations that make it invalid for analyzing realistic biological systems. It also is shown that the more general constraint relationships, while valid, provide nothing new that cannot be obtained directly from the explicit solutions that are available within the larger theory. Thus, one can conclude that approaches based directly on the underlying equations of the system are superior to those based upon constraint relationships as a foundation for the development of physiological genetics.

Genotype↗
PubMed1995

Nonlinear analysis of sleep EEG in depression: calculation of the largest lyapunov exponent.

Conventional sleep analysis according to Rechtschaffen and Kales (1968) has provided meaningful contributions to the understanding of disturbed sleep architecture in depression. However, there is no characteristic alteration of the sleep cycle, which could serve as a highly specific feature for depressive illness. Therefore, we started to investigate nonlinear properties of sleep electroencephalographic (EEG) data in order to elucidate functional alterations other than those obtained from classical sleep analysis. The application of methods from nonlinear dynamical system theory to EEG data has led to the assumption that the EEG can be treated as a deterministic chaotic process. Chaotic systems are characterized by a so-called sensitive dependence on initial conditions. This property can be quantified by calculating the system's Lyapunov exponents, which measure the exponential separation of nearby initial states in phase space. For 15 depressive inpatients (major depressive episodes according to DSM-III-R criteria) and 13 healthy controls, matched in gender, age, and education, we computed the principal Lyapunov exponents L1 of EEG segments corresponding to sleep stages, I, II, III, IV, and rapid eye movement (REM), according to Rechtschaffen and Kales, for the lead positions CZ and PZ. We found statistically significant decreased values of L1 during sleep stage IV in depressives compared with a healthy control group.

Adult↗
PubMedDate not supplied

Controllability of selection-mutation systems.

The well-known Fisher type selection-mutation model is studied from the point of view of mathematical systems theory. Mutation rates are considered as control functions. Based on a general sufficient condition for local controllability of non-linear systems with invariant manifold, a method is proposed to guarantee the controllability of the considered population into a polymorphic equilibrium.

Mutation↗
PubMed2005

Simulation and validation of modelled sphingolipid metabolism in Saccharomyces cerevisiae.

Mathematical models have become a necessary tool for organizing the rapidly increasing amounts of large-scale data on biochemical pathways and for advanced evaluation of their structure and regulation. Most of these models have addressed specific pathways using either stoichiometric or flux-balance analysis, or fully kinetic Michaelis-Menten representations, metabolic control analysis, or biochemical systems theory. So far, the predictions of kinetic models have rarely been tested using direct experimentation. Here, we validate experimentally a biochemical systems theoretical model of sphingolipid metabolism in yeast. Simulations of metabolic fluxes, enzyme deletion and the effects of inositol (a key regulator of phospholipid metabolism) led to predictions that show significant concordance with experimental results generated post hoc. The model also allowed the simulation of the effects of acute perturbations in fatty-acid precursors of sphingolipids, a situation that is not amenable to direct experimentation. The results demonstrate that modelling now allows testable predictions as well as the design and evaluation of hypothetical 'thought experiments' that may generate new metabolomic approaches.

Computer Simulation↗
PubMed1996

Overview: Synchronization and patterns in complex systems.

The theory of complex systems, such as neural assemblies or lattices of chaotic oscillators has generated many new problems including the synchronization or regularization of the cooperative behavior of systems consisting of chaotic elements, regular spatial patterns in "chaotic" lattices, and so on. A number of these problems were discussed at the International School in Nonlinear Science-95 (Nizhniy Novgorod, Russia). In this overview we try to formulate some of the most interesting problems that were discussed at that meeting. (c) 1996 American Institute of Physics.

Journal Article↗
PubMed2001

Modelling and prediction for chaotic fir laser attractor using rational function neural network.

Many real-world systems such as irregular ECG signal, volatility of currency exchange rate and heated fluid reaction exhibit highly complex nonlinear characteristic known as chaos. These chaotic systems cannot be retreated satisfactorily using linear system theory due to its high dimensionality and irregularity. This research focuses on prediction and modelling of chaotic FIR (Far InfraRed) laser system for which the underlying equations are not given. This paper proposed a method for prediction and modelling a chaotic FIR laser time series using rational function neural network. Three network architectures, TDNN (Time Delayed Neural Network), RBF (radial basis function) network and the RF (rational function) network, are also presented. Comparisons between these networks performance show the improvements introduced by the RF network in terms of a decrement in network complexity and better ability of predictability.

Infrared Rays↗
PubMedDate not supplied

[Neurons of the rabbit midbrain reticular formation during a defensive conditioned reflex].

Analysis of unit activity of the midbrain reticular formation was carried out on alert rabbits during defensive conditioning. Most of the examined neurones exhibited phasic responses corresponding in time to the components of the evoked potential (EP) recorded in the cortical visual area in response to the "indifferent" stimulus, and to the conditioned stimulus and electric cutaneous reinforcement. The data obtained are considered from the standpoint of the Anokhin functional systems theory. A conclusion has been made regarding the participation of reticular units in providing all the basic mechanisms of the functional system of the behavioral act. Discharges of one and the same neurone may correspond to different components of the EPs to conditioned and unconditioned stimuli. In different behavioral acts a neurone may apparently participate in different systemic mechanisms.

Animals↗
PubMed1990

Application of entropy measures derived from the ergodic theory of dynamical systems to rat locomotor behavior.

Measures of complexity derived from ergodic theory of dynamical systems were developed and applied to an exemplary data set describing locomotor movements of rats in a bounded space. A symbolic dynamical system was obtained by partitioning the event space into equally probable partition elements, using a k-dimensional tree. The measures calculated from the symbolic sequences included the topological entropy (ht)--i.e., the rate of increase of all possible sequences with increasing sequence length--and the metric entropy (hm)--i.e., the rate of increase of all likely sequences with increasing sequence length. These measures were used to assess changes in rat locomotor behavior as recorded in the behavioral pattern monitor (BPM) that were induced by amphetamine (0.25, 0.50, 1.0, or 2.0 mg/kg) and 3,4-methylenedioxymethamphetamine (MDMA; 1.25, 2.5, 5.0, or 10.0 mg/kg). Amphetamine increased the mean activity, ht, and hm. MDMA resulted in a monotonic dose-response curve for activity but exhibited a biphasic dose response in ht and hm. In particular, some animals in the higher dose groups showed a ht in the range of the saline controls, whereas other animals exhibited a significantly reduced ht and a greater decrease in hm, suggesting that two different behavioral reactions coexist within the same higher dose range of MDMA. An important implication of our method is that, in applied ergodic measure-theoretic approaches, the partition that determines the elements of the symbolic dynamical system should not be specified a priori on abstract mathematical grounds but should be chosen relative to its significance with respect to the data set in question. Here, the animal constructs its own spatiotemporal partition in behavioral phase space.

3,4-Methylenedioxyamphetamine↗
PubMed2004

[The key technology of picosecond time-correlated single photon counting spectrometer].

The picosecond time-correlated single photon counting spectrometer developed uses the TCSPC technique and grating splitter technique that can compensate the time spread dynamically and statically. The time spread caused by the conventional optical system can be eliminated completely. The multichannel analyzer is used to measure the fluorescence decay curves and the time-resolved spectrum by opening the time windows. The method for multi-exponential fitting to the fluorescence decay is also used to deal with the data. The system theory and design of the spectrometer are presented in detail, and the process of operation is introduced with the integration of the system. Many standard samples have been measured, and the data have been analyzed and contrasted. Experimental results show that the fluorescence life-span scaled by the spectrometer reaches picosecond distinction, and the spectrometer's sensitivity is single photon counting. Time resolution of the spectrometer is 8.8 ps.

Equipment Design↗
PubMedDate not supplied

[100 years since the birth of Academician Petr Kuzmic Anohin].

This paper provides a brief biography of an outstanding physiologist and academician Petr Kuzmich Anokhin. With his functional system theory, academician P. K. Anokhin was the first to introduce a systematic approach to discussing functioning of an organism. Principles of functional systems have been applied in technical systems as well.

History, 20th Century↗
PubMed1985

Dynamic quenchers in fluorescently labeled membranes. Theory for quenching in a three-phase system.

The theory for quenching of fluorescently labeled membranes by dynamic quenchers is described for a three-phase system: a fluorescently labeled membrane, a nonlabeled membrane, and an aqueous phase. Two different experimental protocols are possible to determine quenching parameters. Using the first protocol, partition coefficients and bimolecular quenching constants were determined for a hydrophobic quencher in carbazole-labeled membranes in the presence of an unlabeled reference membrane. These parameters determined for 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) using this three-phase analysis were in good agreement with values determined by a two-phase analysis without the reference lipid. Hence, the theory was verified. In the second protocol, the quencher partition coefficient was determined for unlabeled membranes in the presence of a carbazole-labeled reference membrane. Partition coefficients for DDE determined by this method were the same as partition coefficients determined for carbazole-labeled membranes using the two-phase analysis. The greater ease in determining partition coefficients and bimolecular quenching constants by the three-phase analysis and, in particular, the ability to determine the partition coefficient in unlabeled membranes make the three-phase analysis especially useful. This method was used to study the effect varying the membrane lipid composition has on the partition coefficient. The data indicate that partition coefficients of DDE in fluid membranes are not dramatically dependent upon polar head group composition, fatty acid composition, or cholesterol content. However, partitioning into gel-phase lipids is at least 100-fold less than fluid-phase lipids.

Biophysical Phenomena↗
PubMed2002

Integrative medicine and systemic outcomes research: issues in the emergence of a new model for primary health care.

Clinicians and researchers are increasingly using the term integrative medicine to refer to the merging of complementary and alternative medicine (CAM) with conventional biomedicine. However, combination medicine (CAM added to conventional) is not integrative. Integrative medicine represents a higher-order system of systems of care that emphasizes wellness and healing of the entire person (bio-psycho-socio-spiritual dimensions) as primary goals, drawing on both conventional and CAM approaches in the context of a supportive and effective physician-patient relationship. Using the context of integrative medicine, this article outlines the relevance of complex systems theory as an approach to health outcomes research. In this view, health is an emergent property of the person as a complex living system. Within this conceptualization, the whole may exhibit properties that its separate parts do not possess. Thus, unlike biomedical research that typically examines parts of health care and parts of the individual, one at a time, but not the complete system, integrative outcomes research advocates the study of the whole. The whole system includes the patient-provider relationship, multiple conventional and CAM treatments, and the philosophical context of care as the intervention. The systemic outcomes encompass the simultaneous, interactive changes within the whole person.

Complementary Therapies↗
PubMedDate not supplied

An hypothesis paper on practice environment and the provision of health care: could hospital occupancy rates effect quality?

This paper will explore whether hospital occupancy influences quality of care. It discusses the 'systems' theory of error causation in the context of adverse medical outcomes. It then relates how high occupancy rates may cause problems in hospital systems. The evidence relating to quality of care and occupancy is reviewed. Finally, a new method of studying this relationship using time series analysis is proposed. We conclude that the relationship requires further exploration since revealing 'system' problems may compel clinicians to expose problems medical errors.

Bed Occupancy↗
PubMed1994

Ethnological studies of medical sciences.

A broad overview of ethnological (anthropological) methods and theory is presented historically and conceptually. Medical sciences are assumed to be socially produced and reproduced, and a cross-cultural perspectives helps us view them more objectively. Discussion is organized in a framework of general systems theory, and illustrated primarily from recent literature on childbirth. Linkages and communication between different levels of systems: patient, profession, society and ecology, focus on interaction between levels, much of which is ritualized and political.

Communication↗
PubMed2003

[Contribution to the logistic theory of growth: temporal structure and growth potential].

The analysis of a structured population according to three (juvenile, mature and senescent) cellular states is carried out within the framework of Delattre's transformation systems theory. Growth in number, with the dissymmetry of cell divisions, is determined by an autocatalysis process under the constraint of the availability of a source. Two models are presented: their dynamics results in a growth of the exponential type or of the sigmoidal type, respectively. In the sigmoidal case, the logistic equation (Richards-Nelder's function with adjunction of a lower asymptote Y not equal to 0) fits satisfactorily the simulated data of the total cell number Y. The growth potential is defined as the instantaneous capacity of autocatalysis, which is expressed in relation to the present 'mitotic resources' (source + non-senescing mature cells). The acceleration variations d2Y/dt2 are in close agreement with the growth potential gradient. The analysis is then generalized to other population structuring. As a result, the logistic equation can be interpreted in terms of a formal model of growth of a structured population submitted to autocatalysis and competition.

Animals↗