Network structure effects in reservoir computers.

A reservoir computer is a complex nonlinear dynamical system that has been shown to be useful for solving certain problems, such as prediction of chaotic signals, speech recognition, or control of robotic systems. Typically, a reservoir computer is constructed by connecting a large number of nonlinear nodes in a network, driving the nodes with an input signal and using the node outputs to fit a training signal. In this work, we set up reservoirs where the edges (or connections) between all the network nodes are either +1 or 0 and proceed to alter the network structure by flipping some of these edges from +1 to -1. We use this simple network because it turns out to be easy to characterize; we may use the fraction of edges flipped as a measure of how much we have altered the network. In some cases, the network can be rearranged in a finite number of ways without changing its structure; these rearrangements are symmetries of the network, and the number of symmetries is also useful for characterizing the network. We find that changing the number of edges flipped in the network changes the rank of the covariance of a matrix consisting of the time series from the different nodes in the network and speculate that this rank is important for understanding the reservoir computer performance.

Enhancing synchrony in chaotic oscillators by dynamic relaying.

In a chain of mutually coupled oscillators, the coupling threshold for synchronization between the outermost identical oscillators decreases when a type of impurity (in terms of parameter mismatch) is introduced in the inner oscillator(s). The outer oscillators interact indirectly via dynamic relaying, mediated by the inner oscillator(s). We confirm this enhancing of critical coupling in the chaotic regimes of the Lorenz system, in the Rössler system in the absence of coupling delay, and in the Mackey-Glass system with delay coupling. The enhancing effect is experimentally verified in the electronic circuit of Rössler oscillators.

The Bonfils fiberscope: a clinical evaluation of its learning curve and efficacy in difficult airway management.

BACKGROUND: This study evaluated the use of the Bonfils fiberscope by analyzing its learning curve, efficacy and safety during airway management. METHODS: This was a prospective observational study where five anesthetists, with differing levels of experience, were asked to use the Bonfils rigid fiberscope (Karl Storz) for a six-month period. They used the scope when performing endotracheal intubations in patients undergoing general anesthesia. The patients were excluded if various clinical indicators predicted that they might be difficult to intubate. The patient's head was kept in the neutral position to simulate the intubation of a trauma patient. Direct laryngoscopy with a Macintosh blade was performed to assign a Cormack and Lehane grade prior to attempting laryngoscopy with the Bonfils fiberscope. After intubating the patient with the Bonfils fiberscope, intubation time and any complications or failures noted after the procedure were recorded. RESULTS: The study included 216 patients, three of which were failed intubations. No complications occurred during the study period. The median intubation time was 21.4 s. The learning curve improved significantly after 20 intubations (P<0.05) and was affected by the operator's experience and aptitude with endoscopic viewing. Seventeen patients were deemed to have "unpredicted" difficult airways: 15 subjects with a Cormack grade 3 (6.9%) and two subjects with a Cormack 4 (0.9%). Median time to intubation in subjects with a Cormack <3 was 16 s (95% CI=10-29 s), and in subjects with a Cormack ≥3, it was 15 s (CI 95%=15-18 s) with P=0.703. CONCLUSION: The Bonfils fiberscope is an efficient, easy to use and safe device for endotracheal intubation.

Synchronization in dynamical networks: evolution along commutative graphs.

Starting from an initial wiring of connections, we show that the synchronizability of a network can be significantly improved by evolving the graph along a time dependent connectivity matrix. We consider the case of connectivity matrices that commute at all times, and compare several approaches to engineer the corresponding commutative graphs. In particular, we show that synchronization in a dynamical network can be achieved even in the case in which each individual commutative graphs does not give rise to synchronized behavior.

Levobupivacaine and ropivacaine in the infraclavicular brachial plexus block.

AIM: Infraclavicular brachial plexus block were first described by Raj, yet this block remained underutilized despite theoretical advantages. The aim of this prospective, randomized study was to compare equipotent doses of levobupivacaine and ropivacaine. METHODS: For this prospective, randomized study we have enrolled, after informed consent, 30 patients of both sexes, ASA status I-II, who were going to receive surgery to the forearm or hand with tourniquet position on the arm. The infraclavicular plexus block was performed by using vertical technique. The block was performed with 30 mL of levobupivacaine 0.5% or ropivacaine 0.75%. RESULTS: No differences were reported between 2 groups in terms of demographic data. The onset-time for motor block was greater for ropivacaine group (p<0.05); the sensitive block was longer in levobupivacaine group (p<0.05). CONCLUSIONS: The long duration of sensory block associated with the with good analgesia, less toxicity and the pharmacodynamic properties of levobupivacaine include this new local anaesthetic as a valid choice respect other local anaesthetic for infraclavicular plexus block.

Assessing spatial coupling in complex population dynamics using mutual prediction and continuity statistics.

A number of important questions in ecology involve the possibility of interactions or "coupling" among potential components of ecological systems. The basic question of whether two components are coupled (exhibit dynamical interdependence) is relevant to investigations of movement of animals over space, population regulation, food webs and trophic interactions, and is also useful in the design of monitoring programs. For example, in spatially extended systems, coupling among populations in different locations implies the existence of redundant information in the system and the possibility of exploiting this redundancy in the development of spatial sampling designs. One approach to the identification of coupling involves study of the purported mechanisms linking system components. Another approach is based on time series of two potential components of the same system and, in previous ecological work, has relied on linear cross-correlation analysis. Here we present two different attractor-based approaches, continuity and mutual prediction, for determining the degree to which two population time series (e.g., at different spatial locations) are coupled. Both approaches are demonstrated on a one-dimensional predator-prey model system exhibiting complex dynamics. Of particular interest is the spatial asymmetry introduced into the model as linearly declining resource for the prey over the domain of the spatial coordinate. Results from these approaches are then compared to the more standard cross-correlation analysis. In contrast to cross-correlation, both continuity and mutual prediction are clearly able to discern the asymmetry in the flow of information through this system.

Levobupivacaine versus ropivacaine in psoas compartment block and sciatic nerve block in orthopedic surgery of the lower extremity.

AIM: The aim of this study was to compare the clinical profiles of psoas block and sciatic nerve block performed with either 0.5% levobupivacaine or 0.75% ropivacaine. METHODS: With ethical committee approval and written informed consent 80 ASA physical status I-II patients, undergoing lower extremity surgery received intravenous premedication with midazolam (0.05 mg/kg) and atropine (0.01 mg/kg). Patients were randomly allocated to receive a lumbar plexus block with: Levobupivacaine Group (L) 30 ml of 0.5% levobupivacaine or Ropivacaine Group (R) 0.75% ropivacaine, and sciatic nerve block with: Group R 10 ml 0.75 ropivacaine or Group L 0.5% levobupivacaine. The onset time and duration of nerve block were evaluated. RESULTS: The motor onset time was shorter in Group L than in Group R. The motor offset time was similar in the 2 groups, the time being slightly greater for Group R. Group L presented a higher difference of resolution to motor-sensitive block compared to Group R. CONCLUSIONS: The differences between Groups L and R were characterised by: a faster motor onset time in Group L with a longer time between motor and sensitive resolution determining a lower demand for analgesic drugs postoperatively and greater support for motor control recovery.

Controlling system dimension: a class of real systems that obey the Kaplan-Yorke conjecture.

The Kaplan-Yorke conjecture suggests a simple relationship between the fractal dimension of a system and its Lyapunov spectrum. This relationship has important consequences in the broad field of nonlinear dynamics where dimension and Lyapunov exponents are frequently used descriptors of system dynamics. We develop an experimental system with controllable dimension by making use of the Kaplan-Yorke conjecture. A rectangular steel plate is driven with the output of a chaotic oscillator. We controlled the Lyapunov exponents of the driving and then computed the fractal dimension of the plate's response. The Kaplan-Yorke relationship predicted the system's dimension extremely well. This finding strongly suggests that other driven linear systems will behave similarly. The ability to control the dimension of a structure's vibrational response is important in the field of vibration-based structural health monitoring for the robust extraction of damage-sensitive features.

Parameter ranges for the onset of period doubling in the diode resonator.

One of the classic problems in the study of nonlinear dynamics has been the diode resonator. Previous work with the diode resonator sought to explain the causes of period doubling and chaos, and often used simplified models. This paper instead seeks to link the onset of nonlinear dynamical effects to measurable parameters by comparing experiments and numerical models.

Early seizure detection.

For patients with medically intractable epilepsy, there have been few effective alternatives to resective surgery, a destructive, irreversible treatment. A strategy receiving increased attention is using interictal spike patterns and continuous EEG measurements from epileptic patients to predict and ultimately control seizure activity via chemical or electrical control systems. This work compares results of seven linear and nonlinear methods (analysis of power spectra, cross-correlation, principal components, phase, wavelets, correlation integral, and mutual prediction) in detecting the earliest dynamical changes preceding 12 intracranially-recorded seizures from 4 patients. A method of counting standard deviations was used to compare across methods, and the earliest departures from thresholds determined from non-seizure EEG were compared to a neurologist's judgement. For these data, the nonlinear methods offered no predictive advantage over the linear methods. All the methods described here were successful in detecting changes leading to a seizure between one and two minutes before the first changes noted by the neurologist, although analysis of phase correlation proved the most robust. The success of phase analysis may be due in part to its complete insensitivity to amplitude, which may provide a significant source of error.

Detecting functional relationships between simultaneous time series.

We describe a method to characterize the predictability and functionality between two simultaneously generated time series. This nonlinear method requires minimal assumptions and can be applied to data measured either from coupled systems or from different positions on a spatially extended system. This analysis generates a function statistic, Theta(c(0)), that quantifies the level of predictability between two time series. We illustrate the utility of this procedure by presenting results from a computer simulation and two experimental systems.

Functional dependence and quasiperiodicity in the spatiotemporal dynamics of yttrium iron garnet films.

When thin films of yttrium iron garnet (YIG) are placed in a magnetic field and driven at microwave (rf) frequencies, nonlinear interactions within the material cause the normal microwave spin precession to be modulated at lower frequencies. We measure these lower frequency (kHz) signals at two spatially separated locations on the YIG film and use linear and nonlinear analysis to study the functional dependence of the spin dynamics at one location on the spin dynamics at the other location. We see dynamical states where nonlinear analysis can detect a functional dependence that the linear analysis fails to reveal.

Spatiotemporal nonlinear dynamics of a magnetoelastic ribbon.

Magnetoelastic materials have a strong coupling between strain and magnetization, so applying a magnetic field to a magnetoelastic material can change its shape. This coupling leads to interesting dynamics. We have studied the dynamics of a wide ribbon of Metglass 2605sc which was driven by a magnetic field. The ribbon was suspended as a pendulum in a set of Helmholtz coils, which provided both dc and ac magnetic fields. Laser light was reflected off the ribbon to measure its angular displacement. Two points on the ribbon could be simultaneously illuminated, and one of the laser beams could be scanned over the ribbon. We observed quasiperiodic bifurcations in the motion of the ribbon, and characterized the spatial aspect of the motion with some recently developed statistics.

Unifying framework for synchronization of coupled dynamical systems.

A definition of synchronization of coupled dynamical systems is provided. We discuss how such a definition allows one to identify a unifying framework for synchronization of dynamical systems, and show how to encompass some of the different phenomena described so far in the context of synchronization of chaotic systems.

Three coupled oscillators as a universal probe of synchronization stability in coupled oscillator arrays

We show that the stability surface that governs the synchronization of a large class of arrays of identical oscillators can be probed with a simple array of just three identical oscillators. Experimentally this implies that it may be possible to probe the synchronization conditions of many arrays all at the same time. In the process of developing a theory of the three-oscillator probe, we also show that several regimes of asymptotic coupling can be derived for the array classes, including the case of large imaginary coupling, which apparently has not been explored.

Dichhaptic task: methodological factors and brain organization.

Significant effects of shape, sequence of shapes, distractors, order of report and practise were demonstrated in a free recall dichhaptic task with nonsense shapes in adults. A left hand superiority (in accordance with theoretical expectations) was observed only in the second reports of the first half of the test. No sex differences were found. There was a preference to report first the right hand, and the opposite preference was observed in a dichhaptic letter task. It is probable that all these methodological factors may have affected previous dichhaptic studies. The association with other lateral and cognitive parameters is also analysed.

Using multiple attractor chaotic systems for communication.

In recent work with symmetric chaotic systems, we synchronized two such systems with one-way driving. The drive system had two possible attractors, but the response system always synchronized with the drive system. In this work, we show how we may combine two attractor chaotic systems with a multiplexing technique first developed by Tsimring and Suschick to make a simple communications system. We note that our response system is never synchronized to our drive system (not even in a generalized sense), but we are still able to transmit information. We characterize the performance of the communications system when noise is added to the transmitted signal.

Dynamics of transients in yttrium-iron-garnet.

Yttrium-iron-garnet (YIG) is an important technological material used in microwave devices. In this paper we use dual microwave (1-4 GHz) drives to study the dynamical bifurcation behavior of magnetostatic and spin-wave modes in YIG spheres and rectangular films. The samples are placed in a dc magnetic field and driven by cw and pulse-modulated microwave excitations at magnetostatic mode frequencies. A second microwave drive applied to the sample excites additional spin-wave modes that can interact with those arising from the original excitation and thereby affect the transmission characteristics at the primary frequency. We find a significant decrease in transmission of the primary when the secondary frequency is tuned to approximately half that of the primary drive. This decrease is observed both in the steady state behavior and in the initial overshoot transient associated with pulse modulation of the primary excitation. Results such as these are often treated by extending linear theory to include higher order interaction terms. Herein we present a simple dynamical model that reproduces results that qualitatively resemble the experimental data. (c) 1997 American Institute of Physics.

Mechanisms of quenching of the fluorescence of a benzo[a]pyrene tetraol metabolite model compound by 2'-deoxynucleosides.

The hydrophobic interactions of bulky polycyclic aromatic hydrocarbons with nucleic acid bases and the formation of noncovalent complexes with DNA are important in the expressions of the mutagenic and carcinogenic potentials of this class of compounds. The fluorescence of the polycyclic aromatic residues can be employed as a probe of these interactions. In this work, the interactions of the (+)-trans stereoisomer of the tetraol 7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene (BPT), a hydrolysis product of a highly mutagenic and carcinogenic diol epoxide derivative of benzo[a]pyrene, were studied with 2'-deoxynucleosides in aqueous solution by fluorescence and UV spectroscopic techniques. Ground-state complexes between BPT and the purine derivatives 2'-deoxyguanosine (dG), 2'-deoxyadenosine (dA), and 2'-deoxyinosine (dI) are formed with association constants in the range of approximately 40-130 M(-1). Complex formation with the pyrimidine derivatives 2'-deoxythymidine (dT), 2'-deoxycytidine (dC), and 2'-deoxyuridine (dU) is significantly weaker. Whereas dG is a strong quencher of the fluorescence of BPT by both static and dynamic mechanisms (dynamic quenching rate constant k(DYN) = [2.5 +/- 0.4] x 10(9) M(-1)s(-1), which is close to the estimated diffusion-controlled value of approximately 5 x 10(9) M(-1)s(-1), both dA and dI are weak quenchers and form fluorescence-emitting complexes with BPT. The pyrimidine derivatives dC, dU, and dT are efficient dynamic fluorescence quenchers (k(DYN) approximately [1.5-3.0] x 10(9) M (-1)s(-1), with a small static quenching component due to complex formation evident only in the case of dT. None of the four nucleosides dG, dA, dC and dT are dynamic quenchers of BPT in the triplet excited state; the observed lower yields of triplets are attributed to the quenching of single excited states of BPT by 2'-deoxynucleosides without passing through the triplet manifold of BPT. Possible fluorescence quenching mechanisms involving photoinduced electron transfer are discussed. The strong quenching of the fluorescence of BPT by dG, dC and dT accounts for the low fluorescence yields of BPT-native DNA and of pyrene-DNA complexes.