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At least 397 records · Page 22Linked to original sources
PubMed1993

The tricarboxylic acid cycle in Dictyostelium discoideum. Systemic effects of including protein turnover in the current model.

The current model for the tricarboxylic acid cycle in Dictyostelium discoideum is based on extensive experimental studies of enzyme kinetics in vitro and of metabolite fluxes measured in vivo. In the previous papers (Shiraishi, F., and Savageau, M. A. (1992) J. Biol. Chem. 267, 22912-22918; 22919-22925; 22926-22933; 22934-22943) of this series we have carried out extensive analyses of the current model within the framework of biochemical systems theory with a view toward understanding the behavior of the integrated system. The model was found to be ill determined with respect to at least three of its features. In this paper we propose a minimal modification in the model that is consistent with previous experimental data but also includes recycling of amino acids for protein synthesis, one of the neglected features identified as important in the previous analysis. We again perform an analysis within the framework of biochemical systems theory to determine the systemic consequences of this change. The results show that the robustness of the modified model, as determined by the parameter sensitivities, is improved by 2 orders of magnitude over that of the previous model. Analysis of the dynamics shows that the turnover times for the pools of alanine, glutamate, and aspartate are reduced by 2 orders of magnitude and made more physiologically realistic. The distribution of flux is no longer rigidly fixed, and problems previously centered on the metabolism of pyruvate have been partially alleviated. Continued discrepancies lead us to question the degree to which kinetic data obtained with purified enzymes in vitro faithfully reflect the kinetic behavior of the integrated enzyme system in vivo. We must continue to re-examine the manner in which the kinetics of reactions in vivo are represented and to reassess the physical conditions that prevail in vitro and in vivo. Results in this paper direct our attention toward specific aspects of the system where these efforts should be focused. Thus, a minimal modification of the previous model has led to several improvements that make it more representative of the tricarboxylic acid cycle in D. discoideum, and the analysis in this paper leads to further predictions for improving the model.

Animals↗
PubMedDate not supplied

Child development and public policy: toward a dynamic systems perspective.

Little theoretical work exists that proposes general mechanisms for how public policies may influence child development. This article argues that dynamic systems theories may be useful in illuminating such processes, as well as highlighting gaps in current research at the intersection of public policy analysis and developmental science. A brief review of dynamic systems theories as they are currently utilized in other areas of developmental science is provided, as well as a statement of why they may help advance research in public policy and child development. Five principles of dynamic systems theories are presented and discussed using examples from research that address the question, "How do current antipoverty and welfare reform policies affect children?" Also presented are examples of hypotheses and research questions that each principle may generate for future work. The concluding section presents challenges that each principle poses for research methodology, and potential uses of the dynamic systems approach for developing and integrating policy and program initiatives.

Child↗
PubMed1981

Reevaluating the theoretical model underlying the neurodevelopmental theory. A literature review.

The purpose of this paper is to evaluate the foundations of prevalent physical therapy technique based on the current research on motor control. The conceptual framework of the neurodevelopmental theory, as described in the writings of the Bobaths, is presented. Their explanations of central nervous system disorders and recommendations for intervention are based upon a unidirectional model of the nervous system in which postural and voluntary motion become two separate and distinct entities. Systems theory is an alternative model of nervous system structure. In systems theory, the organism is a circular network of interacting yet autonomous subsystems, rather than a vertical structure of descending controls. Relevant research that supports the systems viewpoint is discussed and applied to the theories in the neurodevelopmental approach. Thus, another model is offered for understanding the functioning of the central nervous system when it is intact and when it is in a pathological state.

Animals↗
PubMed2002

Nonlinear interdependence in neural systems: motivation, theory, and relevance.

In this article, we motivate models of medium to large-scale neural activity that place an emphasis on the modular nature of neocortical organization and discuss the occurrence of nonlinear interdependence in such models. On the basis of their functional, anatomical, and physiological properties, it is argued that cortical columns may be treated as the basic dynamical modules of cortical systems. Coupling between these columns is introduced to represent sparse long-range cortical connectivity. Thus, neocortical activity can be modeled as an array of weakly coupled dynamical subsystems. The behavior of such systems is represented by dynamical attractors, which may be fixed point, limit cycle, or chaotic in nature. If all the subsystems are perfectly identical, then the state of identical chaotic synchronization is a possible attractor for the array. Following the introduction of parameter variation across the array, such a state is not possible, although two other important nonlinear interdependences--generalized and phase synchronized--are possible. We suggest that an understanding of nonlinear interdependence may assist advances in models of neural activity and neuroscience time series analysis.

Electroencephalography↗
PubMed2004

A unified theory for systems and cellular memory consolidation.

The time-limited role of the hippocampus for explicit memory storage has been referred to as systems consolidation where learning-related changes occur first in the hippocampus followed by the gradual development of a more distributed memory trace in the neocortex. Recent experiments are beginning to show that learning induces plasticity-related molecular changes in the neocortex as well as in the hippocampus and with a similar time course. Present memory consolidation theories do not account for these findings. In this report, we present a theory (the C theory) that incorporates these new findings, provides an explanation for the length of time for hippocampal dependency, and that can account for the apparent longer consolidation periods in species with larger brains. This theory proposes that a process of cellular consolidation occurs in the hippocampus and in areas of the neocortex during and shortly after learning resulting in long-term memory storage in both areas. For a limited time, the hippocampus is necessary for memory retrieval, a process involving the coordinated reactivation of these areas. This reactivation is later mediated by longer extrahippocampal connectivity between areas. The delay in hippocampal-independent memory retrieval is the time it takes for gene products in these longer extrahippocampal projections to be transported from the soma to tagged synapses by slow axonal transport. This cellular transport event defines the period of hippocampal dependency and, thus, the duration of memory consolidation. The theoretical description for memory consolidation presented in this review provides alternative explanations for several experimental observations and presents a unification of the concepts of systems and cellular memory consolidation.

Animals↗
PubMed1980

A bio-physical basis of mathematics in synaptic function of the nervous system: a theory.

The purpose of this paper is to present a bio-physical basis of mathematics. The essence of the theory is that function in the nervous system is mathematical. The mathematics arises as a result of the interaction of energy (a wave with a precise curvature in space and time) and matter (a molecular or ionic structure with a precise form in space and time). In this interaction, both energy and matter play an active role. That is, the interaction results in a change in form of both energy and matter. There are at least six mathematical operations in a simple synaptic region. It is believed the form of both energy and matter are specific, and their interaction is specific, that is, function in most of the 'mind' and placed where it belongs - in nature and the synaptic regions of the nervous system; it results in both places from a precise interaction between energy (in a precise form) and matter ( in a precise structure).

Action Potentials↗
PubMed2006

Mammalian spore-like cells--a reservoir of spare parts for old-age?

Random exogenous environmental effects--such as radiation and virus--break the biopolymers of the cell (e.g., proteins and DNA), deteriorate its biochemical processes, and eventually cause wear-out and death. Worn-out cells are replaced through the process of cell division. However, a limit to the number of times a cell divides has been noted in all fully differentiated human cell types, as well as in other organisms. While stem cells are an exception and may continue to regenerate cells for the entire lifespan of the organism, they are susceptible too to radiation, infection, and other forms of environmental damage. Spore-like cells are small dormant simple cell-like structures which have the ability to differentiate into mature cells of the tissue from which they are isolated or into the cell types of another tissue. They seem to be present in every tissue in the body. Spore-like cells tolerate conditions that kill differentiated or partially differentiated cells, such as complete oxygen deprivation, and exposure to temperatures which are either much higher or much lower than normal body temperature. When awaken, they can proliferate more rapidly and into more types of differentiated cells than do terminally differentiated cells or stem cells. Reliability theory is a general system theory about systems failure that predicts very well the age-related mortality rates in many species. Reliability theory predicts the late-life mortality deceleration as a consequence of the exhaustion of the redundancy at extreme old-age. The main hypothesis is that the purpose of the spore-like cells is to provide redundancy (i.e., spare parts) for the differentiated and partially differentiated cells in a tissue. Since their use may be required dozens of years after their creation, they need to stay in a dormant and robust state that protects them from deterioration due to detrimental environmental effects. This hypothesis can be validated by measuring the age-related concentration of spore-like cells in various types of tissues and organs. It is predicted that the concentration of spore-like cells in various organs is highly correlated with the health of those organs, especially at old-age. It is expected that tissues with an initially large concentration of spore-like cells may live longer than tissues with an initially small concentration of spore-like cells.

Aging↗
PubMed1983

A systemic-developmental model of day treatment for young adult chronic patients.

The young adult chronic patient is a recently designated dysfunctional group which is growing significantly in numbers. These patients' multiple deficits in independent functioning and their extreme dependence-independence conflict make them difficult to engage and help in traditional forms of outpatient therapy. A day-treatment program which systematically and flexibily intervenes over many levels would seem to increase the likelihood of successful treatment. F. S. DuBois Day Treatment Center, Stamford, Connecticut, has established such a program based on an integration of general systems theory and separation-individuation theory. This systemic-developmental model of day treatment involves both systems-oriented multimodality therapy and developmentally phased expectations for gradually increasing independent functioning. This paper presents theory and applications of the systemic-developmental day-treatment model and a 2-year pilot program evaluation demonstrating its effectiveness.

Adult↗
PubMed2000

A new diagnostic system for psychiatry.

The objective of this work is to apply theoretical concepts from system theories to psychiatry, and formulate a novel diagnostic system that will combine the advantages of descriptive diagnosis and biopsychosocial diagnosis in psychiatry. Biopsychosocial factors and symptoms of mental disorders are described as instabilities and perturbations in a system (i.e. the nervous system). The author reviews certain basic concepts from system theories and applies them to clinical concepts in psychiatry. Biopsychosocial factors are perceived as agitators of organization in the nervous system, and symptoms are described as emergent properties out of these perturbations. A profile of biopsychosocial factors is plotted to correlate with a profile of perturbations and their related symptoms. This agitator versus perturbation mapping is advantageous as a diagnostic system for psychiatry. The proposed diagnostic system is of value in dealing with the clinical complexity of mental disorders, has a potential for increasing predictive validity in psychiatry, and may contribute to etiological brain research of mental disorders.

Diagnostic Techniques and Procedures↗
PubMed1990

Family systems intervention and physical illness.

Family systems theory provides the physician with a comprehensive paradigm to investigate the social and interpersonal context of physical illness. All physical illnesses, particularly life-threatening and chronic ones, profoundly affect the family life of the patient, and the changed family circumstances in turn have impact upon the physically ill patient. This reciprocal interaction between the illness and the family system varies according to the onset, course, outcome, and level of disability. This paper discusses the general application of family systems theory to physical illness as well as the description of the family dimension of acute life-threatening illness, AIDS, chronic illness, chronic neurologic disease, dementia, chronic pain, and cancer in children. We propose that an operational knowledge of theoretical concepts and technical competencies of family systems theory can enhance the therapeutic reach of physicians and other health professionals.

Acquired Immunodeficiency Syndrome↗
PubMed1985

A new method for calculating total respiratory system compliance. Theory and model experiments.

A new method for calculating total respiratory system compliance is described, based on simple modelling of a ventilator-respiratory system circuit that assumes linear characteristics of the circuit parameters compliances and resistances. The method requires only that flow measurement be conducted continuously to obtain compliance, if the internal compliance of the circuit is known beforehand. Model experiments showed that the compliance of a child test lung, calculated from the flow recording, differed at most by 10% from the compliance obtained by separate measurements of pressure and volume under static conditions, over a wide range of respiratory flows and airway resistances.

Child↗
PubMed2005

Improving hollow fiber dialyzer efficiency with a recirculating dialysate system. I: Theory and applicability.

The mathematical theory that underlies a novel non-regenerated recirculating dialysate system (RDS) for improving diffusive clearance in hemodialyzers is presented. The theory states the conditions that hemodialyzers must meet to be suitable in RDS optimization. We have verified the applicability of the RDS for several Cuprophan and polysulfone (PS) commercial dialyzers, showing that PS (synthetic) membranes achieve the highest increments of diffusive clearance. A numerical simulation analysis over more general conditions defined by the dimensionless groups of the system demonstrated that the highest diffusive clearance improvements are achieved in dialyzers operating with a low value of the diffusive mass-transfer area/blood flow rate ratio. This study has provided the base for the assessment of the performance of the RDS as compared to several high-efficiency systems, presented in Part II of this work [M. Prado, L. M. Roa, A. Palma, and J. A. Milan, Ann. Biomed. Eng. (2004) submitted].

Blood Chemical Analysis↗
PubMed2000

The organism and the open system. Ervin Bauer and Ludwig von Bertalanffy.

In this historical treatise two biological-system theories, formulated in the 1920s and 1930s, are roughly sketched. The first part discusses the concept of a thermodynamically open system, as coined by the Russian pathologist Ervin Bauer (1890-1942). Like Bertalanffy, Bauer wanted to prove the specificity of the biological sciences against physics. To achieve this, he postulated the necessity to formulate specific laws of motion which are valid for living matter alone. In the second part of the paper, the organismic-system theory of the Austrian-Canadian philosopher and biologist Ludwig von Bertalanffy (1901-1972) is outlined. The focus of this theory relied on the process dynamics that is inherent inside an organismic system. Both theories exemplify closure models for a living organism from a methodical point of view that distinguishes these earlier models from semantic closure, developed by Howard Pattee as an epistemic clue in solving the enigma of living phenomena. The objective here is to disclose the essential differences between these closure conceptions. To encourage further research on closure, the essay concludes with a few questions concerning clarification of the term.

Biology↗
PubMed2006

The hyper-systemizing, assortative mating theory of autism.

The hyper-systemizing theory of autism proposes that the systemizing mechanism is set too high in people with autism. As a result, they can only cope with highly lawful systems, and cannot cope with systems of high variance or change (such as the social world of other minds). They appear 'change-resistant'. This proposal extends the extreme male brain theory of autism. Finally, evidence is reviewed for autism being the genetic result of assortative mating of two high systemizers.

Asperger Syndrome↗
PubMed1998

Tracking case management accountability: a systems approach.

A review of the evaluation of case management programs in the last two decades reveals a lack of consistency in showing outcome effectiveness. In addition, program evaluation models do not reflect the most prevalent theoretical foundation of case management practice, systems theory. It was the purpose of this article to conceptually establish an evaluation model that reflects systems theory in case management practice, to develop evaluation instruments congruent to collecting data in this model, and then to field-test this evaluation model.

Case Management↗
PubMed2004

Organisational change theory and the use of indicators in general practice.

General practices are making greater use of indicators to help shape and develop organisational arrangements supporting the delivery of health care. Debate continues concerning what exactly such indicators should measure and how they should be used to achieve improvement. Organisational theories can provide an analytical backdrop to inform the design of indicators, critique their construction, and evaluate their use. Systems theory, organisational development, social worlds theory, and complexity theory each has a practical contribution to make to our understanding of how indicators work in prompting quality improvements and why they sometimes don't. This paper argues that systems theory exerts the most influence over the use of indicators. It concludes that a strategic framework for quality improvement should take account of all four theories, recognising the multiple realities that any one approach will fail to reflect.

Family Practice↗
PubMedDate not supplied

The semiotics of control and modeling relations in complex systems.

We provide a conceptual analysis of ideas and principles from the systems theory discourse which underlie Pattee's semantic or semiotic closure, which is itself foundational for a school of theoretical biology derived from systems theory and cybernetics, and is now being related to biological semiotics and explicated in the relational biological school of Rashevsky and Rosen. Atomic control systems and models are described as the canonical forms of semiotic organization, sharing measurement relations, but differing topologically in that control systems are circularly and models linearly related to their environments. Computation in control systems is introduced, motivating hierarchical decomposition, hybrid modeling and control systems, and anticipatory or model-based control. The semiotic relations in complex control systems are described in terms of relational constraints, and rules and laws are distinguished as contingent and necessary functional entailments, respectively. Finally, selection as a meta-level of constraint is introduced as the necessary condition for semantic relations in control systems and models.

Biophysical Phenomena↗
PubMed1981

Family therapy in the treatment of anorexia nervosa: theory and technique.

Family systems theory views anorexia nervosa not only as a product of dysfunctional transactional patterns within a family, but also as a crucial stabilizing element within the family. This paper describes the dysfunctional characteristics of anorexic families as well as the relevance of these characteristics to the anorexic symptoms. Two approaches to the treatment of these families, one developed by Minuchin and the other by Selvini Palazzoli, are described and the compatability of family therapy with individual therapy is briefly discussed.

Adolescent↗