Phase space topography and the Lyapunov exponent of electrocorticograms in partial seizures

Summary Electrocorticograms (ECoG's) from 16 of 68 chronically implanted subdural electrodes, placed over the right temporal cortex in a patient with a right medial temporal focus, were analyzed using methods from nonlinear dynamics. A time series provides information about a large number of pertinent variables, which may be used to explore and characterize the system's dynamics. These variables and their evolution in time produce the phase portrait of the system. The phase spaces for each of 16 electrodes were constructed and from these the largest average Lyapunov exponents (L's), measures of chaoticity of the system (the larger the L, the more chaotic the system is), were estimated over time for every electrode before, in and after the epileptic seizure for three seizures of the same patient. The start of the seizure corresponds to a simultaneous drop in L values obtained at the electrodes nearest the focus. L values for the rest of the electrodes follow. The mean values of L for all electrodes in the postictal state are larger than the ones in the preictal state, denoting a more chaotic state postictally. The lowest values of L occur during the seizure but they are still positive denoting the presence of a chaotic attractor. Based on the procedure for the estimation of L we were able to develop a methodology for detecting prominent spikes in the ECoG. These measures (L^*) calculated over a period of time (10 minutes before to 10 minutes after the seizure outburst) revealed a remarkable coherence of the abrupt transient drops of L^* for the electrodes that showed the inital ictal onset. The L^* values for the electrodes away from the focus exhibited less abrupt transient drops. These results indicate that the largest average Lyapunov exponent L can be useful in seizure detection as well as a discriminatory factor for focus localization in multielectrode analysis.     

Dynamics of the level of deterministic chaos associated with gastric electrical uncoupling in dogs

This study investigated the impact of gastric electrical uncoupling on the dynamics of the level of deterministic chaos in cutaneous gastric electrical signals. Eight-channel electrogastrograms (EGG) were recorded from 16 unconscious dogs. Controlled gastric electrical uncoupling was introduced by circumferentially cutting the whole gastric muscle at two different locations. Three separate 30-min EGG recordings were obtained from each dog in the three different states (basal, after the first cut, and after the second cut). The Lyapunov exponents were calculated from sixteen 6.31-min intervals with 75% overlap obtained from each channel in each state. Inadequate EGG signals from which the Lyapunov exponent could not be reliably calculated were quantitatively discarded. The variance and the standard deviation of the three Lyapunov exponent distributions obtained from each channel were studied, and the mean values were subjected to a Student t-test. In 65.6% of all studied channels, the level of chaos was significantly different (p<0.01) after the first cut compared to the basal state, but no predominant direction of variation was observed (47.7% increment vs. 52.5% decrement). After the second cut, 63.6% of the channels studied showed significantly greater Lyapunov exponent compared to the basal state, and 63.1% exhibited significantly greater (p<0.01) level of chaos compared to the intercut state. The dynamics of the level of deterministic chaos in canine electrogastrograms is highly sensitive to severe gastric electrical uncoupling. Moreover, some channel configurations seem to be more sensitive than others in detecting uncoupling.     

Study of Nonisothermal Crystallization Kinetics of Unstretched and Uniaxially Stretched Electroactive PVDF Composite Films

Incorporation of graphene-based fillers such as graphene oxide (GO) and reduced graphene oxide (rGO) into polyvinylidene fluoride (PVDF) followed by uniaxial stretching can significantly improve their electroactive phase content as well as the dielectric properties. In this study, the nonisothermal crystallization kinetics of unstretched and uniaxially stretched PVDF-GO and PVDF-rGO composite films are investigated through differential scanning calorimetry (DSC) at different cooling rates. Avrami-modified Jeziorney's model is used to understand their crystallization behavior which leads to the nucleation of electroactive crystalline phases in PVDF. Avrami's exponent “n” values in the range of 2–4 are obtained for nonisothermal crystallization of PVDF in different samples which reveal both two- and three-dimensional growth of spherulites in the crystalline region. Kissinger's method is used to calculate the activation energy of crystallization and the results reveal accelerated crystallization of PVDF after addition of GO and rGO fillers followed by uniaxial stretching.     

氯化铅对大麦细胞遗传学毒性的研究

用根尖显微压片法研究了铅对大麦根尖分生细胞的细胞遗传学毒性。结果表明 ,铅能降低正常分裂细胞的有丝分裂指数 ,阻碍了细胞向分化状态发展 ,表现出浓度与时间的叠加抑制效应。铅的毒害还表现为致使染色体畸变 ,产生了铅浓度与时间的叠加诱导效应。 1× 10 12 mol/Lpbcl2 上大麦根尖分生细胞的致死浓度     

Detection of non-linearity in schizophrenic patients using magnetoencephalography

Objective: The aim of this study is to investigate the presence of any non-linearity in the magnetoencephalographic recordings (MEG) from the temporal lobe of schizophrenic patients in comparison with controls, in order to find the differences underlying the brain waves. We calculated the correlation dimension, which is a measure of the complexity of the dynamic system, as well as the first Lyapunov exponent that indicates the system's unpredictability. Methods: The schizophrenic group consisted of 3 men and 7 women aged 23-32 years (mean 27.2, SD=3.5) and the control group of 3 men and 6 women aged 26-35 years (mean 31.6±4.1). There were no significant differences between the two groups as far as age and sex were concerned. None of them received any medication. Results: The analysis of the MEG in the schizophrenic group showed lower dimension complexity and moreover the first Lyapunov exponent presented lower values compared with the corresponding ones in the control group, which means lower information processing. Conclusion: EEG findings as determined by MEG and non-linear analysis may offer important perspectives to better understand brain function in schizophrenia.     

Examining feedback mechanisms of postural control in Chiari Malformation by average wavelet coefficient decomposition and the Hurst exponent

BackgroundChiari Malformation (CM) is a congenital disorder occurring when the cerebellar tonsils descend into the foramen magnum, inhibiting cerebrospinal fluid (CSF) flow, causing headaches, dizziness, difficulty swallowing, muscle weakness, and loss of neuromuscular coordination. While there is no cure, surgical decompression of the hindbrain is used to alleviate symptoms. Loss of postural control is a main symptom reported by these patients; however, no study has examined postural stability in this cohort of patients.Research questionDo patients with CM exhibit impaired postural stability compared to healthy controls?.MethodsTwelve female participants diagnosed with CM performed a postural stability test where six participants had undergone decompression (CM-D) surgery while six had not (CM-ND). Participants stood in Romberg fashion on an AMTI force plate according to an IRB-approved protocol. Postural stability measures were quantified by computing Hurst exponents. These values were determined from the Average Wavelet Coefficient method using a level 12 Symlet-2 wavelet to analyze anterior-posterior (AP) center-ofpressure (COP) trajectories in MATLAB. Identical procedures and analyses were performed on healthy control participants with no known neuromuscular disorders.ResultsCM participants displayed significantly impaired postural stability compared to healthy controls (p = 0.0002). CM-D participants displayed significantly impaired postural stability compared to CM-ND (p = 0.002). CM-D and CM-ND both displayed significantly impaired postural stability compared to controls (p < 0.0001 and p < 0.003, respectively).SignificanceLoss of postural stability is considered a main symptom of CM, however no study has previously quantified human postural control in this cohort of patients. Quantifying this relationship can provide further insight to neurologists studying the disorder and to therapists planning rehabilitation and pain relief methods.     

Global exponential stability of neural networks with time-varying delay based on free-matrix-based integral inequality

This paper is concerned with global exponential stability problem for a class of neural networks with time-varying delays. Using a new proposed inequality called free-matrix-based integral inequality, a less conservative criterion is proposed, which is expressed by linear matrix inequalities. Two numerical examples are given to show the effectiveness and superiority of the obtained criterion.     

A characteristic pattern in the postural sway of unilateral vestibular impaired patients

The statistical properties of the center of pressure (COP) change over time, and -invariant methods of the COP analysis is not sufficient to monitor the changes. Therefore, dynamic temporal information of the COP signals has been important in assessing the postural stability. The purpose of this study was to evaluate the characteristic pattern of time–frequency dynamics during the upright stance in patients with unilateral vestibular dysfunction (UVD). This study included 20 dizzy patients with UVD and age-matched 20 control subjects without any vestibular disorder. The COP signals were collected using a single standard force platform and a spectral analysis including the time–frequency dynamics was carried out on the basis of the maximum entropy method (MEM) by using a segment time series analysis. The power spectral density (PSD) analysis exhibited an exponential decreasing shape (1/f ^−β) when plotted on a double logarithmic scale. The average value of β in the low frequency range of less than 1 Hz in the UVD group was significantly lower than that in the control group (p < 0.05) in the medial-lateral (ML) direction under eyes closed condition. In the segment time series analysis, the peak frequency of the COP signals in the patients with UVD gradually converged to the frequency range of 0.1–0.2 Hz in the ML direction under EC condition. Our results suggest that the segment time series analysis of the COP signals can derive a characteristic pattern related to the UVD. It may indicate an increased reflexivity of the COP fluctuation by the UVD, resulting in inducing the instability.     

Inverse optimal neural control of a class of nonlinear systems with constrained inputs for trajectory tracking

This paper focusses on recurrent adaptive neural control applied to unknown nonlinear systems with input constraints. A recurrent high‐order neural network is used in order to identify the unknown system and a learning law is obtained using the Lyapunov methodology. Then a control law, which stabilizes the reference tracking error dynamics, is developed using the inverse optimal control approach. Tracking error stability is established as a function of design parameters. Chaotic systems are considered to demonstrate the applicability of the approach, via simulations, as for their stabilization and synchronization. The obtained simulation results illustrates the proposed approach capabilities for trajectory tracking of unknown nonlinear systems, whose inputs are constrained. Copyright © 2011 John Wiley & Sons, Ltd.     

Designing first‐in‐human dose of coagulation factors: application of pharmacokinetic allometric scaling

The objectives of this study were to (i) evaluate the predictive performance of pharmacokinetic interspecies scaling of coagulation factors to predict clearance (CL) and (ii) project first‐in‐human dose based on the predicted human CL. Human CL of nine coagulation factors was predicted using two or three animal species using two methods: (i) CL vs. body weight (simple allometry) and where applicable (ii) the product of CL and brain weight vs. body weight. Based on the predicted human CL, four methods were used to project the first‐in‐human dose. The predicted pharmacokinetic parameters and the estimated first‐in‐human dose of coagulation factors were compared with the observed human values obtained from clinical trials. The results of the study indicated that the CL of coagulation factors can be predicted with reasonable accuracy in humans and a good estimate of first‐in‐human dose can be obtained from the predicted human CL. The suggested methods in this study are not only time and cost‐effective but also provide rational alternatives to the somewhat arbitrary dose selection process for coagulation factors often used.