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At least 793 records · Page 44Linked to original sources
PubMed1997

Dynamical systems analysis: a new method of analysing congenital nystagmus waveforms.

Congenital nystagmus is an oculomotor disorder in which fixation is disrupted by rhythmical, bilateral involuntary oscillations. Clinically these eye movements have been described with some degree of success in terms of their peak-to-peak amplitude, frequency, mean velocity and waveform shape. However, it has not proved possible to diagnose any underlying pathology from the nystagmus characteristics. Here, we propose a new approach to understanding the nystagmus using dynamical systems theory. Our approach is based on the use of delay embedding techniques, which allow one to relate a time series of scalar observations to the state space dynamics of the underlying dynamical system. Using this approach we quantify the dynamics of the nystagmus in the region of foveation and present evidence to suggest that it is low-dimensional and deterministic. Our results put new constraints on acceptable models of nystagmus and suggest a way to make a closer link between data analysis and model development. This approach raises the hope that techniques originally developed to stabilise chaotic systems, by using small perturbations, may prove useful in the control of nystagmus.

Adolescent↗
PubMed2006

Robustness: predicting the effects of life history perturbations on stage-structured population dynamics.

Matrix-based models lie at the core of many applications across the physical, engineering and life sciences. In ecology, matrix models arise naturally via population projection matrices (PPM). The eigendata of PPMs provide detailed quantitative and qualitative information on the dynamic behaviour of model populations, especially their asymptotic rates of growth or decline. A fundamental task in modern ecology is to assess the effect that perturbations to life-cycle transition rates of individuals have on such eigendata. The prevailing assessment tools in ecological applications of PPMs are direct matrix simulations of eigendata and linearised extrapolations to the typically non-linear relationship between perturbation magnitude and the resulting matrix eigenvalues. In recent years, mathematical systems theory has developed an analytical framework, called 'Robustness Analysis and Robust Control', encompassing also algorithms and numerical tools. This framework provides a systematic and precise approach to studying perturbations and uncertainty in systems represented by matrices. Here we lay down the foundations and concepts for a 'robustness' inspired approach to predictive analyses in population ecology. We treat a number of application-specific perturbation problems and show how they can be formulated and analysed using these robustness methodologies.

Animals↗
PubMed2000

Analysis of a distributed model of leg coordination. I. Individual coordination mechanisms.

Using tools from discrete dynamical systems theory, we begin a systematic analysis of a distributed model of leg coordination with both biological and robotic applications. In this paper, we clarify the role of individual coordination mechanisms by studying a system of two leg oscillators coupled in one direction by each of the three major mechanisms that have been described for the stick insect Carausius morosus. For each mechanism, we derive analytical return maps, and analyze the behavior of these return maps under iteration in order to determine the asymptotic phase relationship between the two legs. We also derive asymptotic relative phase densities for each mechanism and compare these densities to those obtained from numerical simulations of the model. Our analysis demonstrates that, although each of these mechanisms can individually compress a range of initial conditions into a narrow band of relative phase, this asymptotic relative phase relationship is, in general, only neutrally stable. We also show that the nonlinear dependence of relative phase on walking speed along the body in the full hexapod model can be explained by our analysis. Finally, we provide detailed parameter charts of the range of behavior that each mechanism can produce as coupling strength and walking speed are varied.

Animals↗
PubMedDate not supplied

Models-of-data and models-of-processes in the post-genomic era.

As we are entering the post-genomic era, models-of-data, such as mining and filtering methods for gene sequences and microarrays and the clustering of co-expressed genes, must be complemented with models-of-processes that explain relationships between genomic information and phenomena at biochemical and physiological levels. Many of these models will have the structure of compartment models, whose conceptualization, identification and analysis will fundamentally benefit from the seminal work of John Jacquez. The article indicates with three vignettes that non-linear compartment models in the formulation of biochemical systems theory are viable candidates for post-genomic models-of-processes.

Animals↗
PubMed1995

Strategic planning and the health care supervisor.

This article explores strategic planning from the perspective of the health care supervisor. It analyzes the strategic environment of organizations, the planning process, how to evaluate the strategic plan, and the implementation phase. A strategic planning model is offered as well as a view of the future of strategic planning. The article articulates that strategic planning should emphasize flexibility. The plan needs to be custom designed for the particular organization. Strategic planning is a primary vehicle for health care supervisors to use work teams to further develop organizational effectiveness. Finally, strategic planning is linked to both research and systems theory.

Evaluation Studies as Topic↗
PubMed1997

Constructions of family nursing: a critical exploration.

Increasingly, the 'family' has become more prominent as part of the interest of nursing. However, this interest has not been accompanied by a critical examination of the current models of family nursing. A critical exploration of the construction of family nursing models reveals a problematic reliance on borrowed theories. Systems theoretical approaches have been widely adopted in nursing, yet are infrequently acknowledged as apolitical constructions that act to minimise the impact of the complex social relations surrounding families. Similarly, the uses of developmental theories in family nursing have not explained the implications of their eurocentric and male construction. The adoption of family nursing models may lead to the decontextualised care of the family and subsequently, to paternalistic nursing responses to families.

Adolescent↗
PubMed1998

An information typology for understanding living systems.

It is argued that we can improve our understanding of living systems by focusing on their informational processes. Recent developments, primarily in evolutionary biology, cybernetics and systems theory, suggest that informational processes are of at least two, and probably three, different types; and that the interaction of these types can be seen as a basis for the self-construction of living systems. Following the work of Csanyi and Kampis, a distinction is drawn between referential and nonreferential information. This typology is further extended to include statereferential information. The statereferential type serves to lend stability to informational arrangements (organization) that are viable so that they may be propagated in space and time.

Information Science↗
PubMed1999

Macroergonomic analysis and design for improved safety and quality performance.

Macroergonomics, which emerged historically after sociotechnical systems theory, quality management, and ergonomics, is presented as the basis for a needed integrative methodology. A macroergonomics methodology was presented in some detail to demonstrate how aspects of microergonomics, total quality management (TQM), and sociotechnical systems (STS) can be triangulated in a common approach. In the context of this methodology, quality and safety were presented as 2 of several important performance criteria. To demonstrate aspects of the methodology, 2 case studies were summarized with safety and quality performance results where available. The first case manipulated both personnel and technical factors to achieve a "safety culture" at a nuclear site. The concept of safety culture is defined in INSAG-4 (International Atomic Energy Agency, 1991). as "that assembly of characteristics and attitudes in organizations and individuals which establishes that, as an overriding priority, nuclear plant safety issues receive the attention warranted by their significance." The second case described a tire manufacturing intervention to improve quality (as defined by Sink and Tuttle, 1989) through joint consideration of technical and social factors. It was suggested that macroergonomics can yield greater performance than can be achieved through ergonomic intervention alone. Whereas case studies help to make the case, more rigorous formative and summative research is needed to refine and validate the proposed methodology respectively.

Ergonomics↗
PubMed2002

Periodicity, mixed-mode oscillations, and quasiperiodicity in a rhythm-generating neural network.

We studied patterns of oscillatory neural activity in the network that generates respiratory rhythm in mammals. When isolated in vitro, this network spontaneously generates an inspiratory-related motor rhythm, with stable amplitude from cycle to cycle. We show that progressively elevating neuronal excitability in vitro causes periodic modulation of this inspiratory rhythm, evoking (in order): mixed-mode oscillations, quasiperiodicity, and ultimately disorganized aperiodic activity. Thus, the respiratory network oscillator follows a well defined sequence of behavioral states characterized by dynamical systems theory, which includes discrete stages of periodic and quasiperiodic amplitude modulation and progresses (according to theory) to aperiodic chaos-like behavior. We also observed periodic, mixed-mode periodic, and quasiperiodic breathing patterns in neonatal rodents and human infants in vivo, suggesting that breathing patterns generated by the intact nervous system reflect deterministic neural activity patterns in the underlying rhythm-generating network.

Animals↗
PubMed1999

The AAMFT-Head Start Training Partnership Project: enhancing MFT capacities beyond the family system.

This paper summarizes the experience of a two-year project to promote partnerships between 12 graduate Marriage and Family Therapy (MFT) training programs and their 12 local Head Start partners. The American Association for Marriage and Family Therapy (AAMFT) awarded 9 grants to MFT-Head Start partnerships that had established relationships with each other prior to the project. Three MFT-Head Start pairs that had no preexisting relationship but wanted to develop one received planning grants. The partnership project provided an exciting opportunity for MFT faculty and interns to integrate family systems theory into larger organizational settings and to enhance the capacity of MFTs to serve disadvantaged, low-income, culturally diverse families and the community agencies that work with them. Preparing MFT students to intervene and respond systemically both in organizations and with the families they serve represents a viable alternative to more traditional approaches to MFT that limit the focus to the family system. Survey results and interview data reflect the rich experiences of MFT faculty and supervisors, MFT interns, and Head Start staff. Implementation issues are discussed and recommendations are made to improve the collaboration between MFTs and community-based agencies such as Head Start.

Child, Preschool↗
PubMed1999

Artificial neural networks: a study in clinical psychopharmacology

Controlled trials in clinical psychopharmacology may fail to provide reliable information about the benefit of treatment when the patient is viewed in a real-life setting rather than as part of a well-defined sampling procedure. A viewpoint, rooted in systems theory, is proposed based on the identification of complex relationships among such dimensions as clinician's reasoning, drug properties, and patient's condition. Artificial Neural Network (ANN) technology provides efficient tools for data analysis within a systems-oriented approach. This study proposes a way to predict the outcome of psychopharmacological treatment. Analysis was conducted on retrospective data from clinical records of psychiatric patients treated with moclobemide. Twelve pharmacological, diagnostic, and topological variables were identified as the decisional items considered by six clinicians: age at onset, sex, previous treatment, duration and dose of moclobemide treatment, other drugs, psychiatric diagnosis and other clinical features. Data were binarily coded and transformed into observed frequencies in the sampling space; treatment outcome was binarily scored as the model's target. A Back-Propagation ANN based on the Delta rule with logistic transfer function was used. ANN correctly classified all cases of successful treatment (n = 51, 100%) but only half of the unsuccessful cases (n = 14, 52%). Patterns of response and areas of uncertainty were analyzed in a topological approach.

Journal Article↗
PubMed1980

A psychotherapeutic approach to silent children.

This paper presents through clinical material a practical conceptual framework in the treatment of silent, nonproductive children. Based on systems theory, the therapist is encouraged to routinely take an inclusive view of the child and his world and make a focused evaluation of the meaning of this resistance at several different levels: (a) the greater, nonfamilial social system, (b) the family system, (c) the dyadic relationship with the therapist, and (d) the intrapsychic economy.

Adolescent↗
PubMed2006

The time course of visual afterimages: data and theory.

Sequential viewing of two orthogonally related patterns produces an afterimage of the first pattern (Vidyasagar et al, 1999 Nature 399 422-423; Francis and Rothmayer, 2003 Perception and Psychophysics 65 508-522). We investigated how the timing between the first stimulus (a vertical bar grating) and the second stimulus (a horizontal bar grating) affected the visibility of the afterimage (a perceived vertical grating). As the duration from offset of the first stimulus increased, reports of afterimages decreased. Holding fixed the total time from offset of the first stimulus and increasing the duration from offset of the second stimulus while decreasing the time between the first and second stimuli, caused a decrease in afterimage reports. We interpret this finding in terms of Grossberg's BCS - FCS (boundary contour system--feature contour system) theory. In this theory, the afterimage percept is the result of color complement after-responses in the FCS system interacting with orientation after-responses in the BCS system. The two types of after-responses interact at a stage of neural filling-in to produce the afterimage percept. As the duration between the stimuli increases, the color after-responses weaken so that visible filling-in is less likely to occur. A similar effect occurs for the orientation after-responses but at a faster time scale. Simulations of the model match the experimental data.

Color Perception↗
PubMed1999

Fitness Landscapes and the Precautionary Principle: The Geometry of Environmental Risk.

/ A generalized mathematical model for exploring the implications of the Precautionary Principle is developed. This model draws on recent developments in the field of complex adaptive systems theory. The existence and importance of the Precautionary Principle in the field of environmental law is taken as given and used as justification for the development of models for exploring the principle's implications.The Precautionary Principle is a legal mechanism for managing the environmental risk arising from incomplete scientific knowledge of a proposal's impacts. The Precautionary Principle is applied to actions that carry with them the potential for serious or irreversible environmental change. The model proposed in this paper draws on methods used in a range of disciplines for modeling (potentially highly nonlinear) interactions between multiple parts of a complex system. These methods have been drawn together under the common mathematical umbrella of Fitness Landscape Theory. It is argued that the model, called "Environmental Impact Fitness Landscapes," allows statements about the sensitivity of the gross effect from a set of impacts to be made when the number of impacts in the set, and/or their degree of interaction, is varied. It is argued that this can be achieved through identification of "meta" or "emergent" properties of the set itself, without reference to the specific causal chains determining behavior in specific instances. While such properties are very general, they may at least allow for the parameterization of the effects of sets of impacts where interactions are highly uncertain and empirical data severely limited, i.e., situations that would typically invoke the Precautionary Principle.KEY WORDS: Fitness landscapes; Precautionary Principle; Nonlinear interactions; Graph theoryhttp://link.springer-ny.com/link/service/journals/00267/bibs/24n1p121.html

Journal Article↗
PubMed2002

Geometry of gene expression dynamics.

MOTIVATION: A gene expression trajectory moves through a high dimensional space where each axis represents the mRNA abundance of a different gene. Genome wide gene expression has a dynamic structure, especially in studies of development and temporal response. Both visualization and analyses of such data require an explicit attention to the temporal structure. RESULTS: Using three cell cycle trajectories from Saccharomyces cerevisiae to illustrate, we present several techniques which reveal the geometry of the data. We import phase-delay time plots from chaotic systems theory as a dynamic data visualization device and show how these plots capture important aspects of the trajectories. We construct an objective function to find an optimal two-dimensional projection of the cell cycle, demonstrate that the system returns to this plane after three different initial perturbations, and explore the conditions under which this geometric approach outperforms standard approaches such as singular value decomposition and Fourier analysis. Finally, we show how a geometric analysis can isolate distinct parts of the trajectories, in this case the initial perturbation versus the cell cycle. CONTACT: junhyong.kim@yale.edu

Algorithms↗
PubMed1998

[Chaotic dynamics in medicine].

It has turned out that almost all laws of nature (especially in biology and medicine) are nonlinear. This means that within the mathematical formulation of a law of nature some systems variables are coupled nonlinearly. The field, describing these nonlinear formulation, is referred to as dynamical systems theory or chaos theory. Analytical techniques derived from the field of chaos theory can be useful in characterising stability and complexity of homeostasis parameters (blood pressure, renal vascular, heart rate). It seems, that nonlinear characteristics may play an important role in prediction of some illnesses of the nervous and cardiovascular system.

Cardiovascular Diseases↗
PubMed1983

Sensation seeking, augmenting-reducing, and absolute auditory threshold: a strength-of-the-nervous-system perspective.

The following measures were obtained from 42 student volunteers: the General and the Disinhibition subscales of the Sensation Seeking Scale (Form IV), the Reducer-Augmenter Scale, and the Absolute Auditory Threshold. General sensation seeking correlated significantly with the Reducer-Augmenter Scale, r(40) = .59, p less than .001, and the Absolute Auditory Threshold, r(40) = .45, p less than .005. Both results proved general across sex. These findings, that high-sensation seekers tend to be reducers and to lack sensitivity to weak stimulation, were interpreted as supporting strength-of-the-nervous-system theory more than the formulation of Zuckerman and his associates.

Adolescent↗
PubMed1990

An integrated approach to family therapy training for psychiatric residents.

Unlike nonmedical family therapists, psychiatric family therapists are able to evaluate and treat both the biological and psychosocial components of a problem. They can integrate knowledge of biology, psychopharmacology and individual psychodynamics with family systems theory and family therapy skills. A family therapy training program is presented as a model which prepares psychiatric residents for this unique role. This model emphasizes the importance of having psychiatrists as family therapy teachers, the use of both systems and psychodynamic perspectives in teaching about families, and the principle of presenting concepts and interventive techniques at successively greater levels of difficulty. Illustrative examples are presented. A minimum of two years of family therapy training and supervision is recommended during a four year residency program.

Adult↗