The oculomotor system as a model for the study of neuronal interaction processes

Identified neurons that control eye movements offer an excellent experimental target for the study of Information coding and neuronal interaction processes wíthin the central nervous system. Here are presented some prelimínary results of the motoneuron behaviour during steady eye fíxation, obtained by regressíon and analysis of variance techniques. A flexible information system intended for the systematic acquisitíon and analysis of simultaneous records of neuronal activity and both eyes angular position in a great amount of cells, oriented to the defínition of mathematical models, is also briefly outlíned.

Two-hybrid system as a model to study the interaction of beta-amyloid peptide monomers.

The kinetics of amyloid fibril formation by beta-amyloid peptide (Abeta) are typical of a nucleation-dependent polymerization mechanism. This type of mechanism suggests that the study of the interaction of Abeta with itself can provide some valuable insights into Alzheimer disease amyloidosis. Interaction of Abeta with itself was explored with the yeast two-hybrid system. Fusion proteins were created by linking the Abeta fragment to a LexA DNA-binding domain (bait) and also to a B42 transactivation domain (prey). Protein-protein interactions were measured by expression of these fusion proteins in Saccharomyces cerevisiae harboring lacZ (beta-galactosidase) and LEU2 (leucine utilization) genes under the control of LexA-dependent operators. This approach suggests that the Abeta molecule is capable of interacting with itself in vivo in the yeast cell nucleus. LexA protein fused to the Drosophila protein bicoid (LexA-bicoid) failed to interact with the B42 fragment fused to Abeta, indicating that the observed Abeta-Abeta interaction was specific. Specificity was further shown by the finding that no significant interaction was observed in yeast expressing LexA-Abeta bait when the B42 transactivation domain was fused to an Abeta fragment with Phe-Phe at residues 19 and 20 replaced by Thr-Thr (AbetaTT), a finding that is consistent with in vitro observations made by others. Moreover, when a peptide fragment bearing this substitution was mixed with native Abeta-(1-40), it inhibited formation of fibrils in vitro as examined by electron microscopy. The findings presented in this paper suggest that the two-hybrid system can be used to study the interaction of Abeta monomers and to define the peptide sequences that may be important in nucleation-dependent aggregation.

Can model Hamiltonians describe the electron–electron interaction in π-conjugated systems?: PAH and graphene

Model Hamiltonians have been, and still are, a valuable tool for investigating the electronic structure of systems for which mean field theories work poorly. This review will concentrate on the application of Pariser–Parr–Pople (PPP) and Hubbard Hamiltonians to investigate some relevant properties of polycyclic aromatic hydrocarbons (PAH) and graphene. When presenting these two Hamiltonians we will resort to second quantisation which, although not the way chosen in its original proposal of the former, is much clearer. We will not attempt to be comprehensive, but rather our objective will be to try to provide the reader with information on what kinds of problems they will encounter and what tools they will need to solve them. One of the key issues concerning model Hamiltonians that will be treated in detail is the choice of model parameters. Although model Hamiltonians reduce the complexity of the original Hamiltonian, they cannot be solved in most cases exactly. So, we shall first consider the Hartree–Fock approximation, still the only tool for handling large systems, besides density functional theory (DFT) approaches. We proceed by discussing to what extent one may exactly solve model Hamiltonians and the Lanczos approach. We shall describe the configuration interaction (CI) method, a common technology in quantum chemistry but one rarely used to solve model Hamiltonians. In particular, we propose a variant of the Lanczos method, inspired by CI, that has the novelty of using as the seed of the Lanczos process a mean field (Hartree–Fock) determinant (the method will be named LCI). Two questions of interest related to model Hamiltonians will be discussed: (i) when including long-range interactions, how crucial is including in the Hamiltonian the electronic charge that compensates ion charges? (ii) Is it possible to reduce a Hamiltonian incorporating Coulomb interactions (PPP) to an 'effective' Hamiltonian including only on-site interactions (Hubbard)? The performance of CI will be checked on small molecules. The electronic structure of azulene and fused azulene will be used to illustrate several aspects of the method. As regards graphene, several questions will be considered: (i) paramagnetic versus antiferromagnetic solutions, (ii) forbidden gap versus dot size, (iii) graphene nano-ribbons, and (iv) optical properties.

Instrumentation for measuring pavement-vehicle interaction. Volume II: Digalog Systems operation and maintenance manual, data acquisition system, model DLI 203. Final report.

Federal Highway Administration, Structures and Applied Mechanics Division, Washington, D.C.

A neuro-mechanical model for interpersonal coordination

The present study investigates the coordination between two people oscillating handheld pendulums, with a special emphasis on the influence of the mechanical properties of the effector systems involved. The first part of the study is an experiment in which eight pairs of participants are asked to coordinate the oscillation of their pendulum with the other participant's in an in-phase or antiphase fashion. Two types of pendulums, A and B, having different resonance frequencies (Freq A=0.98 Hz and Freq B=0.64 Hz), were used in different experimental combinations. Results confirm that the preferred frequencies produced by participants while manipulating each pendulum individually were close to the resonance frequencies of the pendulums. In their attempt to synchronize with one another, participants met at common frequencies that were influenced by the mechanical properties of the two pendulums involved. In agreement with previous studies, both the variability of the behavior and the shift in the intended relative phase were found to depend on the task-effector asymmetry, i.e., the difference between the mechanical properties of the effector systems involved. In the second part of the study, we propose a model to account for these results. The model consists of two cross-coupled neuro-mechanical units, each composed of a neural oscillator driving a wrist-pendulum system. Taken individually, each unit reproduced the natural tendency of the participants to freely oscillate a pendulum close to its resonance frequency. When cross-coupled through the vision of the pendulum of the other unit, the two units entrain each other and meet at a common frequency influenced by the mechanical properties of the two pendulums involved. The ability of the proposed model to address the other effects observed as a function of the different conditions of the pendulum and intended mode of coordination is discussed.

Formal analysis of human-computer interaction using model checking

Experiments with simulators allow psychologists to better understand the causes of human errors and build models of cognitive processes to be used in human reliability assessment (HRA). This paper investigates an approach to task failure analysis based on patterns of behaviour, by contrast to more traditional event-based approaches. It considers, as a case study, a formal model of an air traffic control (ATC) system which incorporates controller behaviour. The cognitive model is formalised in the CSP process algebra. Patterns of behaviour are expressed as temporal logic properties. Then a model-checking technique is used to verify whether the decomposition of the operator's behaviour into patterns is sound and complete with respect to the cognitive model. The decomposition is shown to be incomplete and a new behavioural pattern is identified, which appears to have been overlooked in the analysis of the data provided by the experiments with the simulator. This illustrates how formal analysis of operator models can yield fresh insights into how failures may arise in interactive systems.

Binocular interaction:Contrast matching and contrast discrimination are predicted by the same model

How do signals from the 2 eyes combine and interact? Our recent work has challenged earlier schemes in which monocular contrast signals are subject to square-law transduction followed by summation across eyes and binocular gain control. Much more successful was a new 'two-stage' model in which the initial transducer was almost linear and contrast gain control occurred both pre- and post-binocular summation. Here we extend that work by: (i) exploring the two-dimensional stimulus space (defined by left- and right-eye contrasts) more thoroughly, and (ii) performing contrast discrimination and contrast matching tasks for the same stimuli. Twenty-five base-stimuli made from 1 c/deg patches of horizontal grating, were defined by the factorial combination of 5 contrasts for the left eye (0.3-32%) with five contrasts for the right eye (0.3-32%). Other than in contrast, the gratings in the two eyes were identical. In a 2IFC discrimination task, the base-stimuli were masks (pedestals), where the contrast increment was presented to one eye only. In a matching task, the base-stimuli were standards to which observers matched the contrast of either a monocular or binocular test grating. In the model, discrimination depends on the local gradient of the observer's internal contrast-response function, while matching equates the magnitude (rather than gradient) of response to the test and standard. With all model parameters fixed by previous work, the two-stage model successfully predicted both the discrimination and the matching data and was much more successful than linear or quadratic binocular summation models. These results show that performance measures and perception (contrast discrimination and contrast matching) can be understood in the same theoretical framework for binocular contrast vision. © 2007 VSP.

Interaction of quinolone antibiotics with the human intestinal CACO-2 cell model

The transport of a group of quinolone antibiotics across the human intestinal model, Caco-2 cells, was investigated. It was found that the transport of the quinolones generally correlated with the lipophilicity of the compounds, indicating the passive diffusional transcellular processes were involved. However, it was observed that the transport in both directions apical-to-basolateral and basolateral-to-apical was not equivalent, and polarised transport occurred. For all the quinolones studied except, BMS-284756-01, it was found that the basolateral-to-apical transport was significantly greater than the apical-to-basolateral transport. This finding suggested that the quinolones underwent a process of active secretion. The pKas and logPs for the quinolones were determined using potentiometric titrations. The measured logP values were compared with those determined using theoretical methods. The theoretical methods for calculating logP including the Moriguchi method correlated poorly with the measured logP values. Further investigations revealed that there may be an active transporter involved in the apical-to-basolateral transport of quinolones as well. This mechanism was sensitive to competing quinolones, but, it was unaffected by the metabolic inhibitor combination of sodium azide (15mM) with 2-deoxy-D-glucose (50mM). The basolateral-to-apical transport of quinolones was found to be sensitive to inhibition by a number of different inhibitors. The metabolic inhibitors, sodium azide (15mM) with 2-deoxy-D-glucose (50mM) and 2,4-dinitrophenol (1mM), were able to reduce the basolateral-to-apical transport of quinolones. A reduction in temperature from 37°C to 2°C caused an 80-fold decrease in the transport of gatifloxacin in both directions, however, this effect was not sufficient to abolish the greater basolateral-to-apical secretion. As with apical-to-basolateral transport, it was found that quinolones competed with gatifloxacin for basolateral-to-apical transport, both ofloxacin (100μM) and norfloxacin (100μM) significantly (P<0.003) decreased the basolateral-to-apical transport of gatifloxacin; however, ciprofloxacin (100μM and 300μM) had no effect. A number of inhibitors of various transport systems were also investigated. It was found that the anion transport inhibitor, probenecid (100 μM) had a significant inhibitory effect on the basolateral-to-apical transport of ciprofloxacin (P=0.039), while the cation transport inhibitor cimetidine (100μM and 500μM) had no effect. The organic anion exchange inhibitor 4,4'diisothiocyanostilbene-2-2' -disulphonic acid DIDS (400μM) also had a significant inhibitory effect (P=O.O 13). The PgP inhibitor and anion exchange inhibitor verapamil (400Mμ) was able to completely abolish the basolateral-to-apical secretion of gatifloxacin and bring it into line with the apical-to-basolateral flux. In conclusion, the apical-to-basolateral and basolateral-toapical transport of quinolones involved an active component. The basolateral-to-apical secretion was abolished by a verapamil (400μM), a bisubstrate for PgP and the anion transporter.

The development of a computer simulation model of the interaction between the supply and usage of major components in car assembly you use in stock control

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Finite element model calibration of an instrumented RC building based on seismic excitation including non-structural components and soil-structure- interaction

Peer reviewed

THE INFLUENCE OF MOTIVATION ON EMOTION REGULATION AND MOTOR PERFORMANCE: EXAMINATION OF A NEURO-AFFECTIVE MODEL

Mental stress is known to disrupt the execution of motor performance and can lead to decrements in the quality of performance, however, individuals have shown significant differences regarding how fast and well they can perform a skilled task according to how well they can manage stress and emotion. The purpose of this study was to advance our understanding of how the brain modulates emotional reactivity under different motivational states to achieve differential performance in a target shooting task that requires precision visuomotor coordination. In order to study the interactions in emotion regulatory brain areas (i.e. the ventral striatum, amygdala, prefrontal cortex) and the autonomic nervous system, reward and punishment interventions were employed and the resulting behavioral and physiological responses contrasted to observe the changes in shooting performance (i.e. shooting accuracy and stability of aim) and neuro-cognitive processes (i.e. cognitive load and reserve) during the shooting task. Thirty-five participants, aged 18 to 38 years, from the Reserve Officers’ Training Corp (ROTC) at the University of Maryland were recruited to take 30 shots at a bullseye target in three different experimental conditions. In the reward condition, $1 was added to their total balance for every 10-point shot. In the punishment condition, $1 was deducted from their total balance if they did not hit the 10-point area. In the neutral condition, no money was added or deducted from their total balance. When in the reward condition, which was reportedly most enjoyable and least stressful of the conditions, heart rate variability was found to be positively related to shooting scores, inversely related to variability in shooting performance and positively related to alpha power (i.e. less activation) in the left temporal region. In the punishment (and most stressful) condition, an increase in sympathetic response (i.e. increased LF/HF ratio) was positively related to jerking movements as well as variability of placement (on the target) in the shots taken. This, coupled with error monitoring activity in the anterior cingulate cortex, suggests evaluation of self-efficacy might be driving arousal regulation, thus affecting shooting performance. Better performers showed variable, increasing high-alpha power in the temporal region during the aiming period towards taking the shot which could indicate an adaptive strategy of engagement. They also showed lower coherence during hit shots than missed shots which was coupled with reduced jerking movements and better precision and accuracy. Frontal asymmetry measures revealed possible influence of the prefrontal lobe in driving this effect in reward and neutral conditions. The possible interactions, reasons behind these findings and implications are discussed.

Development of a Coupling Model for Fluid-Structure Interaction using the Mesh-free Finite Element Method and the Lattice Boltzmann Method

In the presented thesis work, the meshfree method with distance fields was coupled with the lattice Boltzmann method to obtain solutions of fluid-structure interaction problems. The thesis work involved development and implementation of numerical algorithms, data structure, and software. Numerical and computational properties of the coupling algorithm combining the meshfree method with distance fields and the lattice Boltzmann method were investigated. Convergence and accuracy of the methodology was validated by analytical solutions. The research was focused on fluid-structure interaction solutions in complex, mesh-resistant domains as both the lattice Boltzmann method and the meshfree method with distance fields are particularly adept in these situations. Furthermore, the fluid solution provided by the lattice Boltzmann method is massively scalable, allowing extensive use of cutting edge parallel computing resources to accelerate this phase of the solution process. The meshfree method with distance fields allows for exact satisfaction of boundary conditions making it possible to exactly capture the effects of the fluid field on the solid structure.