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PubMed2004

The concept of "buffering" in systems and control theory: from metaphor to math.

The paradigm of "buffering" is used increasingly for the description of diverse "systemic" phenomena encountered in evolutionary genetics, ecology, integrative physiology, and other areas. However, in this new context, the paradigm has not yet matured into a truly quantitative concept inasmuch as it lacks a corresponding quantitative measure of "systems-level buffering strength". Here, I develop such measures on the basis of a formal and general approach to the quantitation of buffering action. "Systems-level buffering" is shown to be synonymous with "disturbance rejection" in feedback-control systems, and can be quantitated by means of dimensionless proportions between partial flows in two-partitioned systems. The units allow either the time-independent, "static" buffering properties or the time-dependent, "dynamic" ones to be measured. Analogous to this "resistance to change", one can define and measure the "conductance to change"; this quantity corresponds to "set-point tracking" in feedback-control systems. Together, these units provide a systematic framework for the quantitation of buffering action in systems biology, and reveal the common principle behind systems-level buffering, classical acid-base buffering, and multiple other manifestations of buffering.

Acid-Base Equilibrium↗
PubMed1979

Input-output relationship of the Leaky-integrator neuron model.

This paper presents a method of calculating the spike sequence at the output of the Leaky-Integrator Neuron Model (LIM) in response to an arbitrary input stimulus. The calculations have revealed new properties of the initial transient behavior of the LIM, as well as new constraints upon necessary and sufficient conditions for the appearance of spikes with a fixed phase relation to a periodic input. It is also possible to infer what knowledge about the input stimulus can be obtained from a temporal sequence of spikes at the output of the LIM. In the Discussion, neuronal examples are considered which do not encode the transmitted information as a spike rate, but rather monitor the time of occurence of individual spikes by comparison with a reference signal. This relatively common case is not adequately treated by previous descriptions based on system theory; ways are suggested by which the formalism developed here can be used to describe completely, and understand more fully, the performance of such systems.

Action Potentials↗
PubMed1988

Commentary to "Linear and Nonlinear System Approaches in Pharmacokinetics. How much do they have to offer? I. General considerations".

The review by Veng-Pedersen will hopefully stimulate workers in the field to consider systems techniques more thoroughly. As these techniques are well developed in the engineering fields, students should be encouraged to take relevant courses. In this reviewer's opinion, understanding systems theory will allow pharmacokineticists to "cut through the fat" in the derivation of relationships between kinetic phenomena. However, it should be recognized that the system approaches described in Veng-Pedersen's review probably do not by themselves solve the major problems of response approximation and prediction.

Mathematics↗
PubMedDate not supplied

An emergent account of language impairments in children with SLI: implications for assessment and intervention.

While current theoretical accounts of language impairments in children with specific language impairment (SLI) provide clear direction with regard to intervention goal setting, these same accounts say little with regard to the intervention process. Current developments in connectionist modeling and the extension of principles of dynamical systems theory to cognitive and language development have resulted in a new theory of language development known as emergentism. In contrast to traditional formal linguistic accounts, the emergentist view holds that language is a dynamic evolving system that can be represented as a distribution of probabilistic information. Language acquisition, from this perspective, emerges from the child's simultaneous integration of multiple acoustic, linguistic, social and communicative cues within the context of the communicative interaction. An alternative account of SLI grounded within this emergentist view is presented, and preliminary implications are explored with respect to assessment and intervention.

Child↗
PubMed1997

Modeling signal transduction in normal and cancer cells using complex adaptive systems.

As a first approximation, organisms can be defined by the complement of cell types that they possess. Each cell type is defined by its specific collection of signal transduction pathways. While many pathways are common to most cell types (e.g. glycolysis), others are specific to a particular cell type and serve to characterized that cell. Many diseases, including cancer, are characterized by aberrations in general and specific signal-transduction pathways. These pathways are generally intricate and not easily modeled. The formalism of complex adaptive system theory, however, provides the tools by which these pathways can be investigated. By modeling signal-transduction pathways from the viewpoint of complex adaptive systems, a deeper understanding of their intricacies may result. This could eventually lead to novel methods of therapeutic intervention in diseases that arise from aberrant signal transduction.

Adaptation, Physiological↗
PubMed1989

The child's perceptions of familial relationships: convergence between two assessment techniques.

Children's (N = 28) perceptions of familial relationships were investigated with the Family Environment Scale (FES) and the Network of Relationships Inventory (NRI). The FES assesses overall impressions of the family, and the NRI measures perceptions of individual relationships. Because current family systems theory indicates that positive individual relationships within a dyad (e.g., child-mother) should be related to an overall favorable impression of the family system, we hypothesized that these two instruments should demonstrate convergence on selected dimensions. Results indicated that positive or negative relationships with an individual family member were related to how the child perceived the overall family system, supporting our hypothesis.

Adolescent↗
PubMed1977

An experience with a systems approach to curriculum design.

Learning system design, based on general systems theory, is a powerful facilitator for planning and implementing programs of curriculum and instruction. Curriculum planners are directed to a practical consideration of all systems components, and an awareness of their interrelatedness. Specifically they must deal with: Problem areas or barriers to success; the need to define and choose explicit outcomes; ways to make the curriculum operational; and a specific plan for program assessment. The systems process is value free and content free. Values are generated as content is selected and fitted into the system components. Therefore the system input is a crucial factor in the quality of the system. I have attempted to share some aspects of systems methodology which were very useful in the experience of designing a program for the education of gerontological nurse practitioners.

Curriculum↗
PubMedDate not supplied

[Development or the nursing productivity conceptual framework].

This study was performed to develop the conceptual framework of the nursing productivity. The study efforts were made: (1) to define the concept the nursing productivity, (2) to identify the elements of the productivity, and (3) to determine the relationship among the elements. With the aim, the study employed a descriptive analysis by way of reviewing various references related to the subject. The nursing productivity consists of such elements as the nursing efficiency and the nursing effectiveness which are complementary to each other. The nursing efficiency is the quantitative input/output ratio, while the nursing effectiveness represents the integrated outcome of such sub-elements as the degree of accomplishing nursing goals, the quality of nursing service, consumer's satisfaction, and the degree of improvement of nurse's attitude toward the quality care. The nursing productivity can be estimated by summing up the nursing efficiency and the effectiveness. By employing the system theory model, the elements of the nursing productivity consist of three elements; the input, the process, and the output. By the process elements, the system inputs are transformed to the system outputs nursing efficiency and nursing effectiveness which are input to the system, in turn, through feedback mechanism (Figure 4).

Efficiency↗
PubMed2005

Two wrongs make a right: linear increase of accuracy of visually-guided manual pointing, reaching, and height-matching with increase in hand-to-body distance.

Measurements were made of the accuracy of open-loop manual pointing and height-matching to a visual target whose elevation was perceptually mislocalized. Accuracy increased linearly with distance of the hand from the body, approaching complete accuracy at full extension; with the hand close to the body (within the midfrontal plane), the manual errors equaled the magnitude of the perceptual mislocalization. The visual inducing stimulus responsible for the perceptual errors was a single pitched-from-vertical line that was long (50 degrees), eccentrically-located (25 degrees horizontal), and viewed in otherwise total darkness. The line induced perceptual errors in the elevation of a small, circular visual target set to appear at eye level (VPEL), a setting that changed linearly with the change in the line's visual pitch as has been previously reported (pitch: -30 degrees topbackward to 30 degrees topforward); the elevation errors measured by VPEL settings varied systematically with pitch through an 18 degrees range. In a fourth experiment the visual inducing stimulus responsible for the perceptual errors was shown to induce separately-measured errors in the manual setting of the arm to feel horizontal that were also distance-dependent. The distance-dependence of the visually-induced changes in felt arm position accounts quantitatively for the distance-dependence of the manual errors in pointing/reaching and height matching to the visual target: The near equality of the changes in felt horizontal and changes in pointing/reaching with the finger at the end of the fully extended arm is responsible for the manual accuracy of the fully-extended point; with the finger in the midfrontal plane their large difference is responsible for the inaccuracies of the midfrontal-plane point. The results are inconsistent with the widely-held but controversial theory that visual spatial information employed for perception and action are dissociated and different with no illusory visual influence on action. A different two-system theory, the Proximal/Distal model, employing the same signals from vision and from the body-referenced mechanism with different weights for different hand-to-body distances, accounts for both the perceptual and the manual results in the present experiments.

Adaptation, Ocular↗
PubMed2005

Knowledge discovery and system biology in molecular medicine: an application on neurodegenerative diseases.

The possibility to study an organism in terms of system theory has been proposed in the past, but only the advancement of molecular biology techniques allow us to investigate the dynamical properties of a biological system in a more quantitative and rational way than before . These new techniques can gave only the basic level view of an organisms functionality. The comprehension of its dynamical behaviour depends on the possibility to perform a multiple level analysis. Functional genomics has stimulated the interest in the investigation the dynamical behaviour of an organism as a whole. These activities are commonly known as System Biology, and its interests ranges from molecules to organs. One of the more promising applications is the 'disease modeling'. The use of experimental models is a common procedure in pharmacological and clinical researches; today this approach is supported by 'in silico' predictive methods. This investigation can be improved by a combination of experimental and computational tools. The Machine Learning (ML) tools are able to process different heterogeneous data sources, taking into account this peculiarity, they could be fruitfully applied to support a multilevel data processing (molecular, cellular and morphological) that is the prerequisite for the formal model design; these techniques can allow us to extract the knowledge for mathematical model development. The aim of our work is the development and implementation of a system that combines ML and dynamical models simulations. The program is addressed to the virtual analysis of the pathways involved in neurodegenerative diseases. These pathologies are multifactorial diseases and the relevance of the different factors has not yet been well elucidated. This is a very complex task; in order to test the integrative approach our program has been limited to the analysis of the effects of a specific protein, the Cyclin dependent kinase 5 (CDK5) which relies on the induction of neuronal apoptosis. The system has a modular structure centred on a textual knowledge discovery approach. The text mining is the only way to enhance the capability to extract ,from multiple data sources, the information required for the dynamical simulator. The user may access the publically available modules through the following site: http://biocomp.ge.ismac.cnr.it.

Biomedical Research↗
PubMed1978

Family therapy techniques for the family physician.

Since 1960, family therapy has emerged from the general field of psychotherapy as a discipline in itself. An extensive literature has been developed, much of it based on general systems theory. Family physicians have routinely recognized problem families within their practice. Skills and techniques are suggested in this article for introducing changes within a family system.

Adult↗
PubMed1996

Use of methods from chaos theory to quantify a fundamental dysfunction in the behavioral organization of schizophrenic patients.

OBJECTIVE: This study aimed to quantify the complexity of behavioral sequences of patients with schizophrenia and comparison subjects by using methods from nonlinear dynamical systems theory. METHOD: A simple choice task consisting of predicting 500 random right or left appearances of a stimulus was used to obtain binary response sequences in 22 patients with schizophrenia and 16 comparison subjects. Dynamical entropy was measured and the fluctuation spectrum of local subsequence entropies calculated to quantify the degree of interdependency between consecutive responses of patients and comparison subjects. RESULTS: The response sequences generated by the schizophrenic patients exhibited a higher degree of interdependency than those of comparison subjects. Moreover, schizophrenic patients exhibited significantly less consistency in their response selection and ordering, characterized by a greater contribution of both highly perseverative and highly unpredictable subsequences of responses within a test session. CONCLUSIONS: The result of the biological abnormality underlying schizophrenia may not be a simple increase or decrease of neuropsychological or neurobiological functions. Instead, the observed abnormalities in behavioral patterns reflect a quantifiable dysregulation and disorganization of these functions.

Adult↗
PubMed1996

Amplitude frequency characteristics of evoked potentials during sleep: an analysis of the brain's transfer properties in depression.

Classical analysis of the spontaneous sleep EEG in depressive disorder commonly reveals alterations of sleep continuity, number of awakenings, slow-wave sleep, and REM sleep compared to healthy controls; however, conventional analysis can not help understand dynamic differences of the sleep EEG during different sleep stages. In order to elicit qualitative alterations of information processing between depressives and healthy controls, we measured late components of auditory and visual evoked potentials (AEPs and VEPs) during different sleep stages of 15 depressive inpatients and in a sex- and age-matched control group from scalp positions Fz, Cz and Pz. According to linear system theory, we then computed the amplitude frequency characteristic (AFC) from averaged AEPs and VEPs in different sleep stages. These AFCs describe the input/output relation of the system under study leading to a characterization of the transfer properties of the brain during sleep in depression. Our investigations showed that information processing appears characteristically altered in depression during non-REM sleep for both auditory and visual stimulation compared to healthy controls. The transfer properties for processing auditory as well as visual information during REM sleep do not appear dynamically impaired in depressive disorder.

Adult↗
PubMed2001

Bridging epidemiology and demography: theories and themes.

Epidemiology and demography, although both encumbering several theoretical constructs, are generally applied, problem-solving disciplines concerned with the nature and trajectories of defined groups. There are differences between the two disciplines in substantive interests and methodological traditions, however both have comprehensive perspectives and both are deeply concerned with the health, social, and economic well-being of human populations. One way to promote productive interdisciplinary research is to apply or develop scientific theories that exploit the complementary interests and methods of the two disciplines. Several candidate theories and themes are suggested here, including (1) the life course approach as applied to the biology of longevity; (2) the "modernized" Malthusian dilemma; (3) the demographic transition within developing countries; (4) the theory of evolution and its social and biological implications; (5) reciprocal effects of ecological and environmental characteristics on population health and well-being; and (6) systems theory as an approach to population complexity. Other approaches to fostering interdisciplinary investigation between these disciplines include joint course work, specifically targeted research funding initiatives and collaborative development of new population theory. The latter may be particularly important from several perspectives: uniting disciplines to jointly approach common and important scientific problems, providing existing frameworks with which to generate new scientific questions, and promoting enhanced scientific rigor by more tightly linking methods with hypotheses.

Biological Evolution↗
PubMedDate not supplied

Anorexia nervosa and the family: effects on younger sisters to anorexia nervosa patients.

The aim of this study was to describe and analyze the experience of the sister of the anorexia nervosa (AN) patient. This experience was examined in terms of the illness, the sister herself, and relations within the family during the course of coping with AN. A qualitative study method was employed in an attempt to understand the complexity and nature of a younger sister's subjective experience regarding an anorexia patient. Nine sisters of AN patients in the active stage of the illness were interviewed. Data were gathered through in-depth, semi-structured taped interviews and content-analyzed by using the layer system theory. The findings provide the sister's personal perspective in regard to her emotional experience in the shadow of the illness and in regard to the systemic processes that take place in the course of a family's coping with the illness. The findings are divided into six main content categories: (1) structural processes; (2) family dynamic processes; (3) emotional processes; (4) change in life functions; (5) body image; and (6) narrative of the illness. Two theoretical concepts are presented that analyze the reality of the sister as an individual and of the family as a system. The first concept relates to the illness as a new member of the family system. The second concept relates to the sister's emotional experience as one of duality. These two concepts underscore the implications of the illness in terms of placing the sister at risk of developing additional pathological symptoms. The present study provides an in-depth description, explanation, and analysis of the younger sister's experience, thus elucidating risks to her emotional and mental functioning. In addition, it opens a window to the world of a family coping with the illness, and clarifies processes of change taking place within it.

Adolescent↗
PubMed1998

Theory and practice of isoelectric focusing of interacting systems.

The theory of mass transport coupled to reversible protein interactions forms the basis for computer simulation of the isoelectric focusing behavior of several model systems. These include pH-dependent conformational transition, carrier ampholyte-induced interactions and protein-ligand interactions. The computational results compare favorably with experimental observations. In addition, a method is formulated for an isoelectric focusing procedure which enables determination of intrinsic ligand-binding constants for statistical binding of a charged ligand, binding to heterogeneous sites, and cooperative binding.

Ampholyte Mixtures↗
PubMedDate not supplied

Design of metabolic engineering strategies for maximizing L-(-)-carnitine production by Escherichia coli. Integration of the metabolic and bioreactor levels.

In this work metabolic engineering strategies for maximizing L-(-)-carnitine production by Escherichia coli based on the Biochemical System Theory and the Indirect Optimization Method are presented. The model integrates the metabolic and the bioreactor levels using power-law formalism. Based on the S-system model, the Indirect Optimization Method was applied, leading to profiles of parameter values that are compatible with both the physiology of the cells and the bioreactor system operating conditions. This guarantees their viability and fitness and yields higher rates of L-(-)-carnitine production. Experimental results using a high cell density reactor were compared with optimized predictions from the Indirect Optimization Method. When two parameters (the dilution rate and the initial crotonobetaine concentration) were directly changed in the real experimental system to the prescribed optimum values, the system showed better performance in L-(-)-carnitine production (74% increase in production rate), in close agreement with the model's predictions. The model shows control points at macroscopic (reactor operation) and microscopic (molecular) levels where conversion and productivity can be increased. In accordance with the optimized solution, the next logical step to improve the L-(-)-carnitine production rate will involve metabolic engineering of the E. coli strain by overexpressing the carnitine transferase, CaiB, activity and the protein carrier, CaiT, responsible for substrate and product transport in and out of the cell. By this means it is predicted production may be enhanced by up to three times the original value.

Biomass↗
PubMed2002

Developmental trajectories, transitions, and nonlinear dynamical systems: a model of crime deceleration and desistance.

Research on crime-related developmental trajectories is reviewed with outcomes revealing the existence of several trajectories rather than a single general pattern. Each trajectory is marked by transitions that define the pattern's path and direction over time. These anticipated transitions differ from the unanticipated transitions known to precipitate crime deceleration and desistance. Borrowing principles from nonlinear dynamical systems theory--sensitive dependence on initial conditions, chaotic attractors, and self-organization in particular--this article offers a model of crime deceleration and desistance in which belief systems congruent with crime are altered in phases--initiation, transition, maintenance--to create belief systems incongruent with crime. The practical implications of this model are discussed and suggestions for future research are outlined.

Adolescent↗