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PubMed2006

Deterministic approach to robust adaptive learning of fuzzy models.

This study is concerned with the adaptive learning of an interpretable Sugeno-type fuzzy inference system, in a deterministic framework, in the presence of data uncertainties and modeling errors. The authors explore the use of Hinfinity estimation theory and least squares estimation for online learning of membership functions and consequent parameters without making any assumption and requiring a priori knowledge of upper bounds, statistics, and distribution of data uncertainties and modeling errors. The issues of data uncertainties, modeling errors, and time variations have been considered mathematically in a sensible way. The proposed robust approach to the adaptive learning of fuzzy models has been illustrated through the examples of adaptive system identification, time-series prediction, and estimation of an uncertain process.

Algorithms↗
PubMed2005

Deterministic coupling of single quantum dots to single nanocavity modes.

We demonstrate a deterministic approach to the implementation of solid-state cavity quantum electrodynamics (QED) systems based on a precise spatial and spectral overlap between a single self-assembled quantum dot and a photonic crystal membrane nanocavity. By fine-tuning nanocavity modes with a high quality factor into resonance with any given quantum dot exciton, we observed clear signatures of cavity QED (such as the Purcell effect) in all fabricated structures. This approach removes the major hindrances that had limited the application of solid-state cavity QED and enables the realization of experiments previously proposed in the context of quantum information processing.

Journal Article↗
PubMed2006

Allelic divergence precedes and promotes gene duplication.

One of the striking observations from recent whole-genome comparisons is that changes in the number of specialized genes in existing gene families, as opposed to novel taxon-specific gene families, are responsible for the majority of the difference in genome composition between major taxa. Previous models of duplicate gene evolution focused primarily on the role that neutral processes can play in evolutionary divergence after the duplicates are already fixed in the population. By instead including the entire cycle of duplication and divergence, we show that specialized functions are most likely to evolve through strong selection acting on segregating alleles at a single locus, even before the duplicate arises. We show that the fitness relationships that allow divergent alleles to evolve at a single locus largely overlap with the conditions that allow divergence of previously duplicated genes. Thus, a solution to the paradox of the origin of organismal complexity via the expansion of gene families exists in the form of the deterministic spread of novel duplicates via natural selection.

Computer Simulation↗
PubMed1996

A terminal dynamics model of the heartbeat.

It is widely assumed that heartbeat dynamics are chaotic, although there has been no evidence confirming such an opinion, and some evidence to the contrary. Additionally, the deterministic assumptions of such dynamics cannot be demonstrated. An alternative model is presented based upon the notion of terminal dynamics, which can more faithfully represent key features of the heartbeat: namely, piecewise determinism, and singular points between beats, which allow for adaptability while maintaining stability.

Adaptation, Physiological↗
PubMed1998

Nonlinear dynamics of 3 Hz spike-and-wave discharges recorded during typical absence seizures in children.

One-channel routine recordings of the scalp electroencephalogram (EEG) from unmedicated children strictly classified as unprovoked typical (3 c/s) absence seizures were selected. The dynamics of spike-and-wave discharges (SWD) were then examined by means of autocorrelation, correlation dimension, averaged pointwise dimension and largest Lyapunov exponent. For one EEG signal with pronounced spike-and-wave (SW) patterns, these measures were used complementary to a surrogate data method, a nonlinear (SETAR) modeling approach, and a SW simulation procedure providing five types of SW test signals. The SETAR model exhibited stationary SW dynamics, visually very similar to the EEG target signal, and with clear nonlinear structure. According to the results, the EEG episodes investigated represent low-dimensional dynamics, possibly recorded during nonstationary periods. Arguments that justify the assumption of deterministic chaos in our EEG signals were not obtained with the current methods. From the results one may conclude that two global oscillatory modes are present for the model, and three modes are active during the EEG recording period.

Algorithms↗
PubMedDate not supplied

[Simulation modelling of cell systems in definitive and developing tissues].

A review of simulation models of cells is provided, with a description of the basic methods of simulation. The deterministic and stochastic models of cell kinetics are considered on a few examples. A tendency has been revealed to applying the method computer reflection of the structure of heterogeneous cell systems. The utilization of specialized programmed languages of simulation is considered as promising.

Animals↗
PubMed1992

Using multidimensional scaling on data from pairs of relatives to explore the dimensionality of categorical multifactorial traits.

An accurate specification of the dimensionality and ordering of categorical multifactorial phenotypes (e.g., smoking status, including heavy, moderate, light, and nonsmokers) is an important prerequisite for the genetic analysis of these traits. Typically, phenotypic dimensionality and ordering are determined by comparing the relative fits of alternative parametric threshold models. Here, a method of analysis is described which addresses the same issue of trait dimensionality but does not require parametric assumptions. Specifically, we detail how nonmetric multi-dimensional scaling (MDS), applied to contingency tables which cross-classify the phenotypes or responses of one relative with another, may be used to explore trait dimensionality. Scaling results from deterministic simulation studies indicate that the latent structure of categorical phenotypes can be recovered with nonmetric MDS. Results from stochastic simulations, however, indicate that the accuracy of recovery, as well as the rejection of models of incorrect dimensionality, are strongly dependent upon sample size and the latent liability correlation between relatives. As an application of the method, the dimensionality of a measure of smoking status in 1,656 pairs of monozygotic twins ascertained through the American Association of Retired Persons is considered. The MDS results indicate that the onset of the smoking habit and the quantity smoked in this aging population represent a unidimensional process. The implication this finding has for subsequent genetic analysis is discussed.

Aged↗
PubMed2004

Deterministic quantum teleportation of atomic qubits.

Quantum teleportation provides a means to transport quantum information efficiently from one location to another, without the physical transfer of the associated quantum-information carrier. This is achieved by using the non-local correlations of previously distributed, entangled quantum bits (qubits). Teleportation is expected to play an integral role in quantum communication and quantum computation. Previous experimental demonstrations have been implemented with optical systems that used both discrete and continuous variables, and with liquid-state nuclear magnetic resonance. Here we report unconditional teleportation of massive particle qubits using atomic (9Be+) ions confined in a segmented ion trap, which aids individual qubit addressing. We achieve an average fidelity of 78 per cent, which exceeds the fidelity of any protocol that does not use entanglement. This demonstration is also important because it incorporates most of the techniques necessary for scalable quantum information processing in an ion-trap system.

Journal Article↗
PubMed2003

A model of the nuclear control of mitochondrial DNA replication.

Mitochondria are the semi-autonomous organelles that are responsible for generating the majority of the energy required by mammalian cells under normal conditions. They are only semi-autonomous because the replication, transcription and translation of the DNA molecules within the mitochondrion, mtDNA, are ultimately controlled by the cell nucleus. We present a series of three models of the nuclear control of mtDNA replication, with an increasing complexity in the role of mtDNA mutations in the models. We solve these deterministic models exactly, and compare these solutions to the results of stochastic simulations of the same systems. We use the steady states of the deterministic model to explain behaviors, such as threshold effects and mitochondrial proliferation, that are often seen in the cells of patients affected by mitochondrial diseases and that also occur with age. The parameters of these models illustrate the dual control of mitochondria by both the nuclear and mitochondrial DNA.

Animals↗
PubMed2006

Current practices for risk zoning around nuclear power plants in comparison to other industry sectors.

This paper analyses the background and current status of the information basis leading to the definition of risk and emergency zones around nuclear power plants (NPPs) in different countries in Europe and beyond. Although dependable plant-specific probabilistic safety assessment (PSA) of level 2 and/or level 3 could in principle provide sufficiently detailed input to define the geographical dimension of a NPP's risk and emergency zones, the analysis of the status in some European and other countries shows that other, "deterministic" approaches using a reference accident are actually used in practice. Regarding use of level 2 PSA for emergency planning, the approach so far has been to use the level 2 PSA information retrospectively to provide the justification for the choice of reference accident(s) used to define the emergency plans and emergency planning zones (EPZs). There are significant differences in the EPZs that are defined in different countries, ranging from a few up to 80km. There is a striking contrast in the extent of using probabilistic information to define emergency zones between the nuclear and other high risk industry sectors, such as the chemical process industry, and the reasons for these differences are not entirely clear, since the risk of chemical industry is similar as that of the nuclear sector. The differences seem to be more related to risk perception than to the actual risk potential. Therefore, there is a strong need to be able to communicate risk information to the Public both before and following an accident. In addition, there is a need to educate the Public so that they can understand risk information in a comparative sense. Finally, based on the consensus discussions at a recent JRC/OECD International Seminar on Risk and Emergency Zoning around NPPs, a set of recommendations is given in the areas of: -a more comprehensive use of the available risk information for risk zoning purposes, -risk communication; -comparative (energy) risk assessment.

Disaster Planning↗
PubMed2002

Miracles and the limits of medical knowledge.

In considering whether medical miracles occur, the limits of epistemology bring us to confront our metaphysical worldview of medicine and nature in general. This raises epistemological questions of a higher order. David Hume's understanding of miracles as violations of the laws of nature assumes that nature is completely regular, whereas doctrines such as C. S. Peirce's "tychism" hold that there is an element of absolute chance in the workings of the universe. Process philosophy gives yet another view of the working of nature. Physicians have no epistemological grounds for declaring any cure to be miraculous. Miracles are theological (or philosophical) entities, and not medical entities. All physicians can do is to determine whether or not a cure is scientifically inexplicable according to the current epistemological standards of medical science. As these standards change, what is currently unexplainable may become explainable. However, we can also come to realize that our current explanations are in fact unsatisfactory. Our justifications of knowledge claims about miracles will depend on our views about determinism and indeterminism. If the universe is not a deterministic one, we should be open to the possibility of encountering what appear to us as sui generis events. These would not be violations of immutable laws of nature, but manifestations of the true workings of nature, and certainly causes for wonder.

Humans↗
PubMed2000

Production of resistant HIV mutants during antiretroviral therapy.

HIV drug therapy often fails because of the appearance of multidrug-resistant virus. There are two possible scenarios for the outgrowth of multidrug-resistant virus in response to therapy. Resistant virus may preexist at low frequencies in drug-naive patients and is rapidly selected in the presence of drugs. Alternatively, resistant virus is absent at the start of therapy but is generated by residual viral replication during therapy. Currently available experimental methods are generally too insensitive to distinguish between these two scenarios. Here we use deterministic and stochastic models to investigate the origin of multidrug resistance. We quantify the probabilities that resistant mutants preexist, and that resistant mutants are generated during therapy. The models suggest that under a wide range of conditions, treatment failure is most likely caused by the preexistence of resistant mutants.

Anti-HIV Agents↗
PubMed2006

Effect of stochastic synaptic and dendritic dynamics on synaptic plasticity in visual cortex and hippocampus.

Various forms of synaptic plasticity, including spike timing-dependent plasticity, can be accounted for by calcium-dependent models of synaptic plasticity. However, recent results in which synaptic plasticity is induced by multi-spike protocols cannot simply be accounted for by linear superposition of plasticity due to spike pairs or by existing calcium-dependent models. In this paper, we show that multi-spike protocols can be accounted for if, in addition to the dynamics of back-propagating action potentials, stochastic synaptic dynamics are taken into account. We show that a stochastic implementation can account for the data better than a deterministic implementation and is also more robust. Our results demonstrate that differences between experimental results obtained in hippocampus and visual cortex can be accounted for by the different synaptic and dendritic dynamics in these two systems.

Action Potentials↗
PubMed1994

Stochastic simulation and sensitivity analysis: estimating future demand for health resources in China.

A simulation model has been built to estimate the demand for hospital beds and doctors in China between 1990 and 2010. The model was used to compare deterministic sensitivity analysis and stochastic simulation in assessing inherent uncertainty in health projections. The stochastic simulation method uses information more efficiently, and produces a more reasonable average estimate and a more meaningful range of projections than deterministic sensitivity analysis. However, it may be preferable to combine the use of both approaches because they have different, complementary, advantages and disadvantages. The usefulness of 3 value estimates of input variables and the benefits of the triangular distribution for stochastic simulation should be emphasized in health projections.

China↗
PubMed1991

Stochastic versus deterministic in haemopoiesis: what is what?

'Stochastic' models of haemopoiesis are discussed in juxtaposition to 'deterministic' concepts. It is argued that certain characteristic features attributed to stochastic models are conjectures, not supported by the observations quoted to provide an experimental basis: for example, an assumption of extrinsic control and another assumption that such control is inaccessible to external influences up to the very latest stages of cell development. Furthermore, it is argued that quantitative relationships between early progenitors (stem cells) and the number of colonies produced in vitro, cited as evidence supporting the proliferation and differentiation scheme of the stochastic model of random restriction, are also compatible with other models, providing that some sufficiently complex mechanism is involved in the control process. A simple model based on the principle of ordered development (usually denoted 'proliferation tree') is presented as an example and the calculated distributions are shown to have the same form as the experimental ones.

Hematopoiesis↗
PubMedDate not supplied

Neural coding with graded membrane potential changes and spikes.

The neural encoding of sensory stimuli is usually investigated for spike responses, although many neurons are known to convey information by graded membrane potential changes. We compare by model simulations how well different dynamical stimuli can be discriminated on the basis of spiking or graded responses. Although a continuously varying membrane potential contains more information than binary spike trains, we find situations where different stimuli can be better discriminated on the basis of spike responses than on the basis of graded responses. Spikes can be superior to graded membrane potential fluctuations if spikes sharpen the temporal structure of neuronal responses by amplifying fast transients of the membrane potential. Such fast membrane potential changes can be induced deterministically by the stimulus or can be due to membrane potential noise that is influenced in its statistical properties by the stimulus. The graded response mode is superior for discrimination between stimuli on a fine time scale.

Action Potentials↗
PubMed1997

Optimisation in radiotherapy. III: Stochastic optimisation algorithms and conclusions.

This is the final article in a three part examination of optimisation in radiotherapy. Previous articles have established the bases and form of the radiotherapy optimisation problem, and examined certain types of optimisation algorithm, namely, those which perform some form of ordered search of the solution space (mathematical programming), and those which attempt to find the closest feasible solution to the inverse planning problem (deterministic inversion). The current paper examines algorithms which search the space of possible irradiation strategies by stochastic methods. The resulting iterative search methods move about the solution space by sampling random variates, which gradually become more constricted as the algorithm converges upon the optimal solution. This paper also discusses the implementation of optimisation in radiotherapy practice.

Algorithms↗
PubMed1998

Nonlinear dynamic systems evaluation of rhythmic' eye movements (optokinetic nystagmus).

The last decade has seen a surge in the study of nonlinear dynamical behavior in physiologic systems. In this paper, some of the computational techniques most commonly used to investigate the nonlinear dynamics of these systems are described. Applications to eye movement analysis are included, including the validation of a mathematical model of optokinetic nystagmus (OKN) eye movements. OKN appears to have some nonlinear and deterministic component, along with significant randomness. Fast phase starting and ending points are somewhat predictable (deterministic), while so-called 'exceptional events' analysis shows that they also have a large random component. Surrogate data methods suggest that the population of slow and fast phases in OKN is more important than any specific relationship between adjacent slow and fast phases. Analysis of a statistical model for fast phase intervals indicates that the model data are slightly more random than the actual OKN.

Computational Biology↗